Preheat the oven to 350 degrees F. Prepare a 6 inch spring form pan by lining the sides with parchment paper. Melt the chocolate in a small glass bowl, either over a double boiler or in the microwave. If you use the microwave, make sure to only heat it in 30 second intervals, stirring after each time, so as not to burn the chocolate.
Get two small or medium mixing bowls. Make sure one of them is COMPLETELY oil free, as you will be using it to whip egg whites. I always wash the bowl before using it, just in case. Place the softened butter in the other bowl, and using a spatula, mix it until it is smooth. Add the almond flour and stir until completely combined. Add the egg yolks, and put the egg whites in the other (super duper clean) bowl. Mix the egg yolk almond flour mixture well, and add the melted chocolate. Stir until combined, and set aside.
Using a (super duper clean) hand mixer, start beating the egg whites. Once the egg whites start to foam up a bit, add 1/3 of the sugar at a time, beating well after each addition. Beat until stiff peaks form.
Add about 1/4 of the whipped egg whites to the chocolate mixture, and fold in until well combined. Add half of the remaining egg whites and gently fold in, and then add the remainder and gently fold in. Pour into the cake pan, and bake at 350 for a little over 30 minutes, or until a toothpick comes out clean. Remove the springform and peel away the parchment paper. Allow to cool and eat with a dollop of whipped cream.