Preheat oven to 350 degrees. Lightly grease and flour a 9 x 9 inch baking dish. Set aside.
In a mixing bowl combine the melted butter, brown sugar, egg, vanilla, bananas, and pecans.
Then add in the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Stir until combined. The batter will be thick. Spread into the prepared pan.
Bake for about 35 minutes or until a toothpick inserted comes out clean. Cool completely.
For the frosting, mix together the softened butter, powdered sugar, syrup, and vanilla. Mix until smooth and creamy. Spread over the cooled blondies. Sprinkle with chopped pecans.