three 8-inch round cake pans; an 8- to 10-inch cardboard cake circle; a rotating cake wheel; a Barbie doll
For the cake: Preheat the oven to 350 degrees F. Grease and line the bottoms of three 8-inch cake pans with parchment and set aside.
In a large bowl, sift together 4 cups of the flour, the baking powder and cinnamon, then lightly stir in the salt; set aside. In a large measuring cup, whisk together the heavy cream and sour cream and set aside.
In a stand mixer fitted with a paddle attachment, cream together the granulated sugar, butter, coconut oil and lemon zest on medium high until light and fluffy, 3 to 4 minutes. Add the eggs one at a time, beating well after each addition. Add the vanilla and almond extract, if using. Reduce the mixer to medium low and add the dry mixture and cream mixture in 3 alternating additions, mixing until just combined.
Toss the frozen blueberries with the remaining tablespoon of flour and fold them into the batter (don’t rinse the blueberries). Distribute the batter evenly among the cake pans and spread it out evenly (don’t be alarmed if the frozen blueberries cause the cake batter to firm up, that’s ok!).
Bake until the tops of the cakes are starting to brown and a toothpick inserted into the center comes out with a few crumbs on it; begin checking for doneness at 33 minutes and try your darnedest not to let it over-bake. Let cool in the pans for 10 minutes, and then transfer to a wire rack to cool completely.
For the frosting: Combine the frozen blueberries with 2 tablespoons water in a medium saucepan and heat over medium, stirring and mashing occasionally with a rubber spatula, until the blueberries have broken down and released their juices, about 10 minutes. Strain the juices through a fine-mesh sieve into a bowl or measuring cup, using your rubber spatula to mash the blueberries and wring out any juices that they’re still holding onto. You should have around 3 tablespoons of liquid (if it’s much more than that, discard any excess or reserve it for another use).
In a stand mixer fitted with a paddle attachment, beat together the butter and cream cheese until creamy. Gradually add the powdered sugar, then mix in the heavy cream, vanilla, salt and blueberry juice until creamy.
To decorate: Shaping this cake is easiest to do when the layers are cold. So if you have the time, wrap the cake layers in plastic wrap and freeze overnight or even up to a few weeks. (If you don’t have the time, it’s not the end of the world, just make sure the layers are fully cooled.) Use a sharp serrated knife to level the cake layers if they’re not totally flat on top and save the scraps in a large bowl. (If the cakes are frozen too solid to cut, you can let them thaw at room temp for a few minutes so they soften just slightly.)
Place an 8- to 10-inch cardboard cake circle on a rotating cake wheel and add a small dollop of frosting to “glue” on the first layer. Add the first layer of cake, followed by a thin layer of frosting, another layer of cake, another thin layer of frosting and the third layer of cake. Use a thin knife to cut a hole down the center of the cake that’s just big enough for a Barbie doll. Try not to make the hole too big so that she doesn’t flop around. Shove her in! The cake will only come up to her thighs at this point but fear not, the rest will be filled in by cake scraps.
Now it’s time to carve the cake. Use a serrated knife to slowly carve away the cake into the shape of a skirt. Start at the top and shave it off gradually, cutting away from yourself and down the bottom, transferring your scraps to the scrap bowl. Leave about 1 1/2 inches of uncarved cake all around the top to allow room to build up the remaining skirt with your scraps. This doesn’t need to be perfect AT ALL! Frosting will cover up any imperfections! Once you’ve got a general skirt shape, use your hands to mush up the scraps in the bowl. The frosting and the cake’s moisture should help them stick together into a dough-like consistency, but if they're too dry, add a plop of frosting. Pack the cake dough firmly on top of the cake to build the skirt up to reach Barbie’s waist (or higher to be an empire waist! Or a low-rise waist! You are your own fashion designer!).
Take a step back to look at the general shape of the skirt and make any adjustments you’d like: carve off some more for a slimmer skirt, add some Victorian-era dimension with some cake dough, etc.
And then frost! Frost all over with thick swoops of frosting. Swirl in food coloring to create a groovy tie dye look, add sprinkles for a bedazzled look or get out your piping bags and pipe a whole lace wedding dress if that’s your vision.