1Preheat oven to 350℉ (180℃). Coat a 8-inch round or square baking pan with nonstick cooking spray.
2In a large mixing bowl, with electric mixer, cream butter and brown sugar. Beat in egg, buttermilk, vanilla, and mashed banana until blended.
3In a bowl, combine dry ingredients and spices.
4Mix the dry ingredients into the butter mixture until moistened. Do not overbeat.
5Pour batter into prepared pan and spread evenly. Bake 25 to 30 minutes, or until a wooden skewer poked into middle of cake comes out clean.
6Cool in pan on wire rack for about 20 minutes. Can be left in pan or inverted onto cake plate.
Can be frosted, but I serve it plain, with a scoop of vanilla ice cream, or a dollop of vanilla yogurt or drizzle of caramel ice cream topping.