Almond and Chocolate Flourless Cake

Preheat the oven to 350 degrees F. Generously coat a 9" springform pan with 2 teaspoons of the butter and dust with 1 tablespoon of the cocoa (don't tap out the excess cocoa; leave it in the pan.
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In a food processor, combine the blanched almonds with 2 tablespoons of the sugar.
Process until finely ground.
In the top of a double boiler over barely simmering water, melt the chocolate and the remaining 4 teaspoons butter, stirring occasionally, until smooth.
Remove from the heat.
Place the chocolate mixture in a large bowl.
Add the almond mixture, sour cream, egg yolks, vanilla extract, almond extract (if using), 1/2 cup of the remaining sugar, and the remaining 2 tablespoons cocoa.
Stir until well-blended.
In a large bowl, with an electric mixer on high speed, beat the egg whites and salt until frothy.
Gradually add the remaining 1/4 cup sugar, beating until stiff glossy peaks form.
Stir one-quarter of the beaten whites into the chocolate mixture to lighten it.
Gently fold in the remaining whites until no white streaks remain.
Place in the prepared pan.
Gently smooth the top.
Bake for 30 minutes, or until the cake has risen, is dry on the top, and a wooden pick inserted in the center comes out with a few moist crumbs.
Place in the pan on a rack and cool until warm.
The cake will fall dramatically.
Loosen the edges of the cake with a knife and remove the pan sides.
Sprinkle with the toasted almonds, if using.