Brownie Bottom Cheesecake

1/2 cup (1 stick) butter
4 squares Unsweetened Baking Chocolate
2-1/4 cups sugar, divided
5 eggs, divided
1/4 cup milk
2 teaspoons vanilla, divided
1 cup flour
1/2 tsp. salt
3 pkg. (8 oz. each) cream cheese, softened
1/2 cup sour cream

Melt butter and chocolate in 3-quart saucepan on very low heat, stirring constantly; cool. Blend in 1-1/2 cups sugar.

Add 2 of the eggs, 1 at a time, mixing on low speed after each addition just until blended. Blend in milk and 1 tsp. of the vanilla. Mix flour and salt; add to chocolate mixture, mixing just until blended. Spread evenly into greased and floured 9-inch springform pan. Bake at 325 degrees for 25 minutes.

Mix cream cheese, remaining 3/4 cup sugar and remaining 1 teaspoon vanilla with electric mixer on medium speed until well blended. Add remaining 3 eggs, 1 at a time, mixing on low speed after each addition just until blended. Blend in sour cream; pour over brownie bottom. (Filling will almost come to top of pan.)

Bake at 325 degrees for 55 to 60 minutes or until center is almost set. Run knife or metal spatula around rim of pan to loosen cake; cool before removing rim of pan. Refrigerate 4 hours or overnight. Let stand at room temperature 30 minutes before serving.