* 8 oz packages, or 24 oz total Preheat oven to 450 degrees sour cream and 2 teaspoons vanilla in large mixer bowl; beat on medium speed until smooth. Add flour, 1 tablespoon at a time, blending well. Add eggs; beat well. In a small bowl, combine cocoa and 1/4 cup sugar. Add oil, 1/2 teaspoon vanilla and 1-1/2 cups of the cream cheese mixture; mix until well blended. Aternately spoon plain and chocolate mixtures into prepared crust, ending with dollops of the chocolate on top; gently swirl with knife or spatula for a marbled effect. Bake at 450 degrees for 10 minutes; without opening oven door, lower temperature to 250 degrees and continue cooking for 30 minutes more. Without opening oven door, turn off heat and let cheesecake sit in oven for 30 minutes. Remove from oven and loosen sides with knife. Let cool and chill.