Brownie Crust
3 oz Unsweetened Chocolate --
Chopped
1/4 c  Unsalted Butter -- cut in
sm Pieces
1/2 c  Flour
1/8 ts Baking Powder
2    Eggs
1 c  Light Brown Sugar -- firmly
Packed
1 1/2 ts Vanilla
2 oz Semisweet Chocolate --
Finely chopped
Filling
8 oz Cream Cheese -- softened
1/2 c  Light Brown Sugar -- firmly
Packed
3    Eggs
1/2 c  Sour Cream
1 1/3 c  Creamy Peanut Butter
1/4 c  Flour
Topping
3/4 c  Sour Cream
3 ts Sugar

For the crust:

Preheat oven to 350.

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 beater 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.