Whisk together the cream and sugar in a pan. Cook over medium-low heat until it begins to simmer

Whisk together the egg yolks, cornstarch, and vanilla extract in a large metal bowl

Pour a third of the whipped cream mixture into the egg yolk mixture, whisking constantly.  Once combined, add the rest of the cream mixture in thirds. Transfer back the custard back into the pot and cook over medium-low heat until the mixture has thickened. This may take up to five minutes.  Be careful to not let the eggs curdle or begin to form chunks. To make that happen, you may need to cook the egg mixture on the lowest heat.

Transfer the custard back to a mixing bowl, cover with a plastic wrap or parchment paper and place into the fridge to cool. 

Pre-heat the oven to 350℉ 

Grease and flour a  8" round springform pan.

Using a stand mixer, a hand mixer, or a whisk if you're feeling ambitious, beat the egg whites until stiff. Add half of the sugar over the egg whites and beat to combine.

Whisk in one half of the almond flour. Do not worry if the egg whites deflate a bit. 

With a spatula, fold in the remaining sugar, almond flour, and gluten-free flour. Pour the batter into the springform pans and for 25 minutes. The cake will be ready when the top has turned a golden brown and a toothpick inserted into the center comes out clean. 

Let the cake cool for 10 minutes before turning out onto a wire rack to cool completely. 

Take the cooled custard out of the fridge and beat together the softened butter with the custard and a pinch of salt until light and fluffy. If it seems too soft, chill in the fridge for 20 minutes then try beating it again.

Assemble the cake. Enjoy the leftover custard slathered on the cake slices.