Bars:
1/2 cup (1 stick) butter, softened
1 cup dark brown sugar, packed
1 egg
1 tablespoon dark rum or 1 teaspoon rum extract
1 cup flour
1/8 teaspoon baking soda
1/2 teaspoon baking powder
1 teaspoon cinnamon
1/4 teaspoon salt
1 cup bananas, diced
1/2 cup (2 ounces) pecans or walnuts, chopped

Frosting:
2 tablespoons unsalted butter at room temperature
4 ounces cream cheese, softened
1/4 cup light brown sugar, packed
1 teaspoon rum or pure vanilla extract
1 teaspoon cinnamon
1 to 2 cups confectioners' sugar, sifted
pecan halves for garnish