Heat oven to 300°F. Lightly grease sides only of 10-inch springform pan.
Stir together all crust ingredients except 1/2 cup toffee bits in bowl. Press crumb mixture evenly on bottom and 1-inch up sides of prepared pan.
Bake 10-12 minutes or until edges are lightly browned. Remove from oven; immediately sprinkle 1/2 cup toffee bits on hot, partially baked crust.
Combine 1 cup sugar and cream cheese in bowl. Beat at medium speed, scraping bowl occasionally, until creamy. Add eggs; continue beating until well mixed. Do not over beat. Pour over crust. Bake 70-75 minutes or until edges are set and lightly browned. Center will move slightly when side of pan is tapped.
Loosen cheesecake from side of pan by running greased knife around inside of pan. Immediately sprinkle 1/4 cup toffee bits and 1/4 cup chopped pecans on top. Cool 1 hour on cooling rack at room temperature. Refrigerate in pan, uncovered, 3-4 hours or until thoroughly chilled. Cover; refrigerate until serving.
Melt 1/4 cup butter in 2-quart saucepan over medium heat; stir in 2/3 cup brown sugar, whipping cream and corn syrup. Cook, stirring occasionally, until mixture just comes to a boil. Boil 3 minutes. Remove from heat.
Add chocolate; stir until melted and smooth. Stir in vanilla. Cool slightly; place in microwave-safe bowl. Cover; refrigerate until serving time.
Just before serving, microwave sauce, stirring every 30 seconds, until warm.
Loosen side of cheesecake by running knife around inside of pan. Carefully remove side of pan. Dip knife in warm water for easier cutting. Clean knife after each cut. Serve sauce over cheesecake slices.