Make existing cheesecake recipe chocolate?
Some additional digging with more specific search terms turned up this recipe: http://www.kraftrecipes.com/recipes/philadelphia-new-york-chocolate-cheesecake-52676.aspx which is effectively exactly what I suggested doing. The only difference is that the number of eggs used is decreased by one, and, of course, the recipe doesn't use any chocolate extract. So apparently I was on the right track :)


  5 pkg. (8 oz. each) PHILADELPHIA Cream Cheese, softened
  1 cup sugar
  3 Tbsp. flour
  1 Tbsp. vanilla
  2 pkg. (4 oz. each) BAKER'S Semi-Sweet Chocolate, broken into pieces, melted, slightly cooled
  1 cup BREAKSTONE'S or KNUDSEN Sour Cream
  3 eggs
  
  Beat cream cheese, 1 cup sugar, the flour and vanilla in large bowl with electric mixer on medium speed until well blended. Add melted chocolate and sour cream; mix well. Add eggs, one at a time, mixing on low speed after each addition just until blended. Pour over crust.
  Bake 1 hour 5 min. to 1 hour 10 min. or until center is almost set. Run knife around rim of pan to loosen cake; cool before removing rim of pan. Refrigerate at least 4 hours or overnight. Store leftover cheesecake in refrigerator.