Pre-heat oven to 350°F. Coat a 9-inch round cake pan with nonstick spray with flour.
Melt butter and chocolate together in microwave, let cool, and then pour into bowl of a standing mixer fitted with a paddle attachment.
Add sugar, turn on to medium high, and then add eggs and egg yolk one at a time, mixing well after each addition.
Add blended cottage cheese, sour cream, vanilla and salt. Beat to combine.
Stop mixer. Sift flour and baking powder over wet ingredients. Beat until smooth, scraping bowl as needed (about 2minutes). Batter will be thick.
Pour into cake pan. Tap lightly on countertop to remove air pockets, if desired.
Bake 40-50 minutes or until a toothpick inserted in center comes out with a few moist crumbs attached. Start testing at 40 minutes as the batter sets quickly.
Let cool 20 minutes in pan. Remove from the pan and transfer to serving dish finish cooling.
Dust with powdered sugar before serving and garnish as desired.