Preheat oven to 350 F. Grease a 13x9-inch baking pan; set aside.
In a large, heavy saucepan, melt butter.
Once butter is partially melted, stir in brown sugar. Continue cooking until melted.
Stir in vanilla and eggs until well-combined.
Add flour, cinnamon, baking powder, baking soda, and salt. Stir until combined.
Pour into prepared baking dish.
Bake for about 45 minutes
Brush warm bars with 1 tablespoon melted butter.
Stir together remaining sugar and cinnamon. Sprinkle bars with cinnamon-sugar mixture.
Let bars cool, and cut into squares to serve.