Preheat oven to 350ºF.
To make Brownies, combine butter, oil and chocolate in a large saucepan over low heat. Heat just until chocolate and butter are melted. Remove from heat and beat in sugar, corn syrup, eggs and vanilla until smooth. Add flour, baking powder and salt. Stir in chocolate chips and nuts, if desired.
Pour brownie batter into greased 12-inch pizza pan. Bake for 14 to 18 minutes until center is just set. Cool on wire rack at least 30 minutes before frosting.
To make Frosting, beat butter, corn syrup, vanilla and salt in a large mixing bowl until light and fluffy. Add powdered sugar and gradually add milk until frosting is desired spreading consistency. Beat in orange coloring until desired shade of orange.
Frost brownies. Make a jack-o-lantern face using candies.