Preheat oven to 325 F. Combine cake mix and butter in large bowl; beat with electric mixer at medium speed just until crumbly. Remove 1 cup mixture. Press remaining mixture evenly into ungreased 13x9-inch baking pan to form crust. Bake 10 minutes; cool on wire rack. Combine cream cheese and peanut butter in large bowl; beat with electric mixer at medium speed until fluffy. Beat in eggs, one at a time, scraping down side of bowl occasionally. Gradually beat in sugar until light. Spoon filling over cooled crust. Combine reserved cake mix mixture and peanuts; spread evenly over filling. Bake 45 minutes or until cake is just set and knife inserted into center comes out clean. Remove from oven; cool at room temperature 30 minutes. Chill at least 2 hours before serving. Drizzle with melted chocolate, if desired.