Preheat oven to 350F.
Melt butter. Transfer to lg mixing bowl.
Add brown sugar; blend well.
Beat in eggs.
Blend in vanilla.
In a separate bowl, blend flour, granulated sugar, baking powder, salt, and cinnamon. Gradually blend into butter mixture.
Mix in mix-ins.
Spread batter evenly into greased 13x9" baking pan.
Bake at 350F until fork tines come out clean, approx. 25-28 minutes.
Cool. Cut and serve.