Preheat oven to 350°F. Prepare your cake pan by greasing and coating it with flour, and line the bottom with parchment paper.
Cream the butter and ⅔ cup of sugar together until fluffy.
Add the egg yolks and beat until blended.
In your mixer bowl, add the egg whites and 1 Tbsp sugar until stiff peaks form. This is about 10-15 minutes on medium speed.
In your microwave-safe bowl, melt the chocolate. Stir this into the butter and sugar mixture.
Add the almond flour and almond extract tot he chocolate mixture and stir to combine.
Once your egg whites are beaten, take about ¼ of them and stir them into the chocolate mix.
Carefully fold in another quarter of the egg whites, and add ⅓ of the cake flour. Repeat until all of the egg whites and flour are added.
Pour the batter into your prepared cake pan.
Bake for 18-25 minutes, depending on your oven. Mine took about 20.