Place 12-inch square sheet of foil on rack below center oven rack in oven. Heat oven to 325°F. In medium bowl, combine crust ingredients; mix well. Press in bottom and about 1 inch up sides of ungreased 10-inch springform pan. Refrigerate while preparing filling.
Beat cream cheese in large bowl with electric mixer at medium speed until smooth. Gradually add 1/2 cup sugar, beating until smooth. Add eggs, 1 at a time, beating well after each addition. Quickly add melted chips, whipping cream and vanilla; beat until smooth. Pour into crust-lined pan.
Bake at 325°F. for 55 to 65 minutes or until edges are set; center of cheesecake will be soft. Turn oven off; open oven door at least 4 inches. Let cheesecake sit in oven for 30 minutes or until center is set.
Remove cheesecake from oven. Cool in pan on wire rack for 1 hour or until completely cooled. Carefully remove sides of pan. Refrigerate at least 4 hours or overnight.
In small heavy saucepan, combine chocolate chips, 1 tablespoon butter and boiling water. Let stand 5 minutes. Whisk chocolate mixture until smooth. Add 3/4 cup sugar and corn syrup; mix well. Bring to a boil over medium-low heat, stirring constantly. Reduce heat to low; boil 8 minutes without stirring.
Remove saucepan from heat. Stir 1/2 teaspoon vanilla into chocolate sauce. Cool 15 minutes, stirring frequently. Sauce will thicken as it cools. Serve cheesecake with sauce. Store cheesecake and sauce in refrigerator.