This cake is really, really good. It's my husband's all-time favorite birthday cake. What I like most is that it tastes like a classic vanilla layer cake - you forget that it is gluten-free. The cake has a moist texture, rich flavor and golden color, thanks to the almond flour. I paired the cake layers with a classic chocolate frosting.
Butter a springform pan (20cm/8in) and line it with parchment paper, cut to fit. Butter the parchment paper. Place the pan on a baking sheet and side aside.
Measure all the ingredients.
In a large mixing bowl, beat the egg yolks at high speed until pale yellow and light. Reduce the speed to moderately low and beat in rum and half of the confectioners' sugar. Turn off the mixer, scrape down bowl, turn the mixer back on and beat on high speed until pale and thick, about 3 minutes. Reduce speed to low and gradually add almond and coconut flours and mix until just combined. Set aside.
In another large (and clean) bowl, whip egg whites, cream of tartar and salt on moderate speed until the beginning stages of soft peaks. Gradually add the remaining confectioners' sugar, one tablespoon at a time. Increase speed to moderately high and beat until whites hold glossy, stiff peaks.
Gently fold the beaten egg whites into the yolk mixture. Pour the batter immediately into a prepared pan. Smooth out the top with an offset spatula.
Bake until the cake is golden brown and a toothpick inserted in the center comes out clean, about 35 minutes. If the top gets too golden but the cake is not yet done, cover the top with a lightly buttered piece of aluminum foil.
Cool the cake completely, at least 1 hour. It may slightly deflate as it cools.
While the cake is cooling, make the frosting as per the recipe.
When ready to assemble, take the cake out of the springform pan. Invert it onto a cutting board, remove the springform bottom, peel off the parchment circle, and slice the cake horizontally into two layers using a long, serrated bread knife (see photos).
To decorate, place a cake layer on a serving plate – the top of the cake should now be the bottom. To keep the plate clean while frosting the cake, tuck 4 strips of parchment paper under the edges of the cake. With a spatula or spoon, dollop a generous amount of frosting onto the top of the cake layer. Use an offset spatula to create a thick, even layer of frosting. Place the second cake layer on top. Generously apply frosting to the top and sides of the cake. Use an offset spatula to even out the top and sides, forming an even layer of frosting. Press sprinkles or other decoration on the sides of the cake. You also can pipe extra frosting on the top/sides of the cake. Remove the parchment strips after you have decorated the cake. [Note: I used a cake cardboard and a cake stand to frost and decorate the cake. I moved the cake to a serving plate afterwards.]
Serve! Store leftovers well wrapped at room temperature (or in the refrigerator if you live in a warm climate) for up to 4 days. I think the cake tastes best a day or two after it is made, when the cake and frosting have had time to meld together.