This is a from-scratch brownie cheesecake, and the best I've ever had. A great ending if you are part of a progressive dinner group and you have the dessert. Four hour to overnight refrigeration required.
Melt butter and chocolate in a 3-quart heavy saucepan on very low heat, stirring constantly; cool. Blend in 1 1/2 cups of the sugar. Add 2 of the eggs, 1 at a time, mixing on low speed after each addition 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 onto bottom of greased and floured 9-inch spring-form pan.
Bake at 325° for 25 minutes.
Mix cream cheese, remaining 3/4 cup sugar and 1 tsp 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° for 55-60 minutes or until center is almost set. Run knife or metal spatula around rim of pan to loosed cake; cool before removing rim of pan. Refrigerate 4 hours or overnight. Let stand at room temperature 30 minutes before serving.