Preheat oven to 350ºF. Spray a 13 x 9-inch baking pan with cooking spray.

CRUST: Combine flour, corn starch, powdered sugar and salt in a large bowl. Add butter and beat with mixer at medium speed until mixture resembles coarse crumbs; press firmly into bottom and 1/4-inch up side of prepared pan.

Bake 15 to 17 minutes or until golden brown. While crust is baking, prepare fudge filling.

FUDGE FILLING: Melt 1/2 cup chocolate chips and 2 tablespoons butter in a medium saucepan over low heat, stirring occasionally. Remove from heat; stir in oil, brown sugar and granulated sugar. Add eggs, one at a time. Stir in flour, salt, vanilla, remaining 1/2 cup chocolate chips and pecans, if desired.

Pour filling over hot crust. Return to oven and bake 20 minutes or until just set. (Bake 3 to 5 minutes longer for firmer bars.) Cool completely on wire rack before cutting into bars.