Preheat the oven to 350 degree F. Lightly butter a 10 inch baking pan.
In a double boiler, heat the butter with the chocolate and stir as it melts until the chocolate has completely melted. Add the espresso, and allow to cool for 5 minutes.
In a large mixing bowl, beat the egg yolks with the sugar until very light and fluffy. Add the cornstarch, baking powder, and almonds. Mix in the chocolate mixture and stir until well combined.
In a separate bowl, beat the egg whites until stiff. Fold the whites into the chocolate mixture until blended. Pour the cake batter into the prepared pan and bake for about 30 minutes. When a skewer is inserted into the cake it should still have a little chocolate mixture sticking to it. If it comes out completely clean the cake has baked a little too long.
Cool 10 minutes and then remove from the cake pan. Cool to room temperature. Serve by topping each slice with a dollop of whipped cream and then garnish with a little powdered cocoa