Peanut Butter and Brownie Cheesecake

Brownie Crust:

3 ounces unsweetened chocolate, chopped

1/4 cup butter, cut into small pieces

1/2 cup sifted all-purpose flour

1/4 teaspoon salt

1/4 teaspoon baking powder

2 large eggs

1 cup firmly-packed light brown sugar

1-1/2 teaspoons vanilla extract

1/2 ounce bittersweet chocolate, finely chopped

Filling:

12 ounces cream cheese, room temperature

1 cup firmly packed light brown sugar

3 large eggs

1-1/3 cups peanut butter

1/2 cup sour cream

Topping:

3/4 cup sour cream

2 teaspoons sugar

1/2 cup creamy peanut butter (optional)

For crust: Position rack in center of oven and preheat to 360 degrees F (170C). Butter a 9 inch diameter springform pan. Dust pan lightly with flour. Melt chocolate and butter. Cool. Blend flour, salt and baking powder in small  bowl. Beat eggs and sugar in bowl until ribbon forms when beaters are lifted, about 4 minutes. Scrape down sides of bowl. Beat in chocolate, vanilla and chopped chocolate. Add dry ingredients and mix until just blended; do not overbeat. Spread 1 cup batter over bottom of pan. Bake until firm, about 17-20 minutes. Cool crust in the freezer, about 15 minutes.Maintain oven temperature. 

Prepare filling: Blend cream cheese and sugar until smooth. Add eggs and sour cream and beat until smooth. Blend in peanut butter. Using small knife, spread remaining brownie batter evenly around sides of pan, sealing to bottom crust. Pour in filling, which will not be as high as brownie batter. Bake until the center is gently set and brownie sides have fallen to form a 1 inch wide ring around the filling, about 30 minutes. For topping: Blend sour cream and sugar in a small bowl. Spread evenly over cheesecake to cover (you may or may not add peanut butter to topping). Bake 3 more minutes. Set cake on rack. Using small, sharp knife, cut around top edge of cake to loosen from pan sides. Cool completely. Loosen cake with a knife and release from the pan. Refrigerate until 1/2 hour before serving time.