Preheat oven to 350° F.

Beat butter at medium speed with an electric mixture until creamy. Add ½ cup sugar, and vanilla, beating well. Gradually add flour, beating at low speed until blended. Stir in pistachios. Press into bottom and 1½ inches up sides of a 9-inch springform pan. Bake for 15 minutes or until golden brown. Cool on a wire rack.

Beat cream cheese at medium speed with an electric mixer until light and fluffy. Gradually add 1½ cups sugar, beating well. Add eggs, one at a time, beating just until yellow disappears. Stir in remaining 2 teaspoons vanilla. Do not overmix.

Pour half of batter into prepared crust; sprinkle with chocolate morsels to within ¾ inch of the edge. Pour in remaining batter, starting at outer edge and working toward center. Place cheesecake on a baking sheet. Bake for one hour or until set. Cool cheesecake on a wire rack for one hour.

Serve slightly warm with sweetened whipped cream if desired. Note: Individual pieces can be warmed in microwave for 30 seconds before serving. Yield: 12 servings.