Upside-Down Clementine Cake | Recipe Test

March 28, 2026

If you've never seen The Secret Life of Walter Mitty, add it to your watch list for this week! It's a little wacky at first, but give it a chance, and you might really enjoy it. The story is very heartfelt and really makes you think about life and traveling...I won't give too much away.

But anyways, an important food from this movie is Walter's mom's clementine cake! After a little research, I discovered that clementine cake is generally made by boiling whole clementines, mashing them, and adding them to a cake batter made with almond flour.

I really want to work more on developing my own recipes. I know that it takes a lot of time with trial and error, research, and tiny adjustments. It's technical... but I'm an engineer, and I'm pretty good at technical things. So today is Trial #1 of Clementine Cake. I will walk you through my process and why I made certain decisions. There is also an actual readable recipe at the end of the post! Spoiler: the cake turned out really yummy. I don't think you're supposed to say the recipe is perfect after only one trial, but it's really scrumptious. I highly recommend you try it!

I'm Not Patient

When researching published recipes for clementine cake, there were two things that stood out to me.

The clementines had to be boiled whole for at least 2 hours on the stove in order for them to be soft enough to mash.
The cake is traditionally made gluten-free with only almond flour. However, I did find a couple of recipes that used only all-purpose flour.

I used this Bakes by Brown Sugar recipe as my base guide to build off of with several changes (https://bakesbybrownsugar.com/clementine-cake-recipe/). Although this was one of the only recipes that didn't boil their clementines, I knew that I needed to soften mine somehow. I only had a weak blender to use to blitz them that would not be able to handle raw whole clementines. But I'm lazy and impatient and didn't want to wait 2 hours for them to be ready. So, I decided to try to use the microwave instead.

To soften my clementines, I pricked the skin several times with the end of a meat thermometer (it was actually very useful), but you could also just do this with a fork or a knife. I then microwaved them for around 8 minutes on high. This made them quite hot but nicely soft. I transferred them to the blender but realized that there was still no way they were going to blend up. I ended up adding the sour cream from the recipe, as well as 60ml of milk (a new addition). Eventually, I was able to pulse it enough to a smoothie-like consistency. There were some bigger chunks of the peel, so I just took those out and left the small pieces (no bigger than a pea).

I knew I didn't want the cake to be 100% almond flour. I enjoy almond flour cakes because of their flavor and moistness but sometimes feel like they can be a little too dense for me. I decided I would go for a 50:50 flour to almond flour ratio, hoping that it would give me a good fluffy cake that was still moist and flavorful. I made sure to increase the quantities of these ingredients slightly to account for the increase in liquid from the new addition of milk.

In the movie, the cake is made in a round pan and is topped with what I assume are candied clementine slices. When I looked up how to make these, it once again involved boiling clementines for an absurd amount of time! This made me think: what if I made the cake an upside-down cake? This way, I could add clementines to the bottom of the pan with some sugar, then have them perfectly cooked once the cake was done and turned out.

I didn't fill my pan all the way because I got nervous it would overflow (it didn't, haha), but I had some extra batter which I baked into two upside-down cupcakes. These were DELICIOUS (dare I say just as good if not better than the main product??). The ratio of the fruit to cake is perfect. If I ever have to make something for a tea party or a lunch, I will 100% be making these.

Here is the recipe for this trial of the clementine cake. It turned out really delicious. It was so moist and had a really nice bite that had a delicious clementine flavor. I'm biased, but I highly recommend you try it!

Upside-Down Clementine Cake Recipe

Prep Time: 40 minutes Cook Time: 40 minutes Assembly Time: 60-90 minutes (including cooling)

Equipment: 8"x4" loaf pan, food processor or blender, digital scale

Cake Ingredients:

95g all-purpose flour
95g almond flour
1/2 tsp salt
1 tsp baking powder
170g whole clementines (approximately 2 medium-sized) + 1 additional clementine for the bottom of the pan
60g full-fat sour cream (room temperature)
60ml milk (2% or whole)
1 tsp vanilla extract
113g butter (room temperature, I honestly used salted butter and the final cake wasn't overly salty)
200g sugar + 1 tablespoon for the pan
2 large eggs (room temperature)

Icing Ingredients:

150g powdered sugar
1 tablespoon sour cream
Zest of 1 clementine (keep some to sprinkle on top of the final cake)
Juice of 1 clementine
Milk (to desired consistancy)

Cake Instructions:

Wash your whole clementines. You should need 4 for this recipe unless they are very small or very large.

Take 2 of the whole clementines and prick them several times all around with either a meat thermometer tip, sharp knife, or fork. Make sure that you prick through the full peel, otherwise the clementines could explode in the microwave.

Place the clementines in a microwave-safe bowl. Microwave on high for 8 minutes. Once done, take out and let cool for around 10 minutes.

In the meantime, whisk the flour, almond flour, baking powder, and salt together in a medium-size mixing bowl.

Once you are able to handle the clementines (please be careful!), break them apart with your hands and place them in the food processor or blender. Pulse the best you can around 15 times, it will be a bit tricky.

Add the sour cream and milk to the pulsed clementines. Continue pulsing until you are able to blend the mixture so it looks almost like a smoothie. It's ok if you can't get it completely smooth. Once you get it as smooth as possible, pour it into a bowl and take out any large pieces of peel. You don't want any pieces bigger than a pea. Add the vanilla and mix to combine.

Preheat the oven to 350 F/175 C.

Place room-temperature butter into a large mixing bowl. Beat with a spatula until very smooth and creamy, around 1 minute. You could also do this with a stand mixer set to medium, but it is doable by hand. Add the 200g sugar and beat until the mixture is smooth and fluffy, around 2 minutes.

Add each egg one at a time to the mixture, beating until each egg is completely incorporated. Make sure to scrape the bottom of the bowl to ensure that everything is well mixed.

Add the flour mixture to the bowl and mix (low speed if using a stand mixer) until 60–70% is combined. Add the clementine mixture and mix (low speed if using a stand mixer) until you can no longer see any dry flour or pockets of liquid. Scrape the bottom of the bowl a few times to ensure everything is combined.

Spray your loaf pan with baking spray and line it with parchment paper. Sprinkle 1 tbsp of sugar onto the bottom of the pan. Take 1 clementine and cut it into horizontal slices, around 1/4-inch thick. Take 4–5 slices (they can overlap slightly) and place them in the pan on top of the sugar. Pour the batter carefully into the pan. Use a spatula to even out the top.

Bake at 350°F for around 35-45 minutes, rotating halfway through. The color should be a deep golden brown. Check doneness with a toothpick or a knife. Remember not to place your tester all the way to the bottom of the pan; it will come out wet if it touches the fruit at the bottom.

Take the cake out of the oven and let it cool initially for 15 minutes (if you wait too much longer, the sugar at the bottom might solidify and make it hard to turn out). Place a wire cooling rack over the pan and invert the cake. Carefully peel the parchment off, ensuring that the fruit doesn't rip off the bottom. Let the cake cool completely (60–90 minutes).

Glaze Instructions:

Place powdered sugar in a mixing bowl. Add the zest of one clementine (keep a tiny bit of leftover zest), the juice of that same clementine, and the sour cream.

Add a small splash of milk and begin mixing the glaze. Add additional milk to reach your desired consistency. Only add small splashes of milk at a time (no more than 1 tsp) to avoid making the glaze too thin too quickly.

Take the glaze and pour it over the cooled cake. Top the cake with a final sprinkling of clementine zest.

For Next Time

This cake was so good. I think the crumb on it is perfect (if I do say so myself). I think one of the main things I want to improve is the amount of clementine on the bottom of the cake. I want more fruit. Maybe I can line the entire pan with slices of clementine? The ratio of fruit to cake in the cupcakes that I tested with the batter was really good, and I want to replicate that for the cake. For Trial #1, though, I will take this as a win. Hopefully, I can develop it further and post an updated recipe in the future!