3 oz unsweetened chocolate, chopped
1/4 cup unsalted butter, cut in small pieces
1/2 cup flour
1/8 teaspoon baking powder
1 cup light brown sugar, firmly packed
1-1/2 teaspoon vanilla
2 oz semisweet chocolate, finely chopped
8 oz cream cheese, softened
1/2 cup light brown sugar, firmly packed
1/2 cup sour cream
1-1/3 cup creamy peanut butter
1/4 cup flour
3/4 cup sour cream
3 teaspoons sugar
For the crust: Preheat oven to 350ºF. Grease a 9-inch springform pan. Dust with flour. Melt unsweetened chocolate and butter in small saucepan over low heat. Cool. Beat eggs and sugar in medium bowl until slowly dissolving ribbon forms when beaters are lifted, about 4 minutes. Beat in melted chocolate mixture, vanilla, and chopped chocolate. Add flour and baking powder. Mix until just blended - do not overbeat. Spread 1 cup brownie batter over bottom of pan. Bake until firm, about 17 minutes. Cool baked crust in freezer for about 15 minutes. Maintain oven temperature.
For the filling: Blend cream cheese and sugar until smooth. Add eggs and sour cream. Add peanut butter and flour. Using small knife, spread remaining brownie batter around the sides of the pan, sealing batter to
bottom crust. Pour in filling, which will not be as high as brownie batter. Bake until center of cheesecake is gently set and brownie sides have fallen to form a ring around the filling - about 50 minutes.
For topping: Blend sour cream and sugar. Spread on top of cheesecake to
within 3/4 inch of edge. Bake cheesecake 3 more minutes.