Sift almond flour and powdered sugar into egg whites.
Fold the dry ingredients in until just combined.
Pour into an 8" round, parchment paper lined cake pan.
Bake at 350F for 25-30 minutes or until golden.
Allow to cool to room temperature.
In a saucepan, combine the egg yolks, heavy whipping cream, granulated sugar and vanilla extract.
Cook over low-medium heat until the custard simmers and thickens (about 5-10 minutes).
Remove the pan from the heat and add the butter in cubes. Stir until combined.
Pour the custard over the almond cake (while still in the pan).
Refrigerate until set (about 2-3 hours).
Drizzle with melted chocolate.
Notes
Start with a perfectly clean bowl: This may seem like a no-brainer but even a little bit of grease can keep your egg whites from achieving stiff peaks. Whatever you use, making sure it’s been thoroughly scrubbed with warm, soapy water.
Don’t use plastics bowls: To the point above, it’s very hard to completely remove fats from plastic bowls and kitchen utensils, which tend to develop a greasy coating over time. Instead, use a glass, metal or ceramic bowl.
Crack your eggs into a separate bowl: Egg yolks = fat and as we’ve established, fats will keep your egg whites from reaching they're full potential. To avoid having a single yolk ruin the whole bowl, be sure to crack and separate your eggs over a small bowl before adding your whites to the bowl you plan to whip them in.
Storage: This cake can be kept in the refrigerator for 2-3 days.