Caramel-Walnut Upsidedown Banana Cake

Spray 8-inch round cake pan with 2-inch-high sides with nonstick spray. Bring butter, sugar, and corn syrup to boil in medium saucepan, stirring constantly until butter melts. Boil syrup 1 minute. Stir in nuts.

Spread topping in prepared pan.

Let topping cool completely.

Preheat oven to 350°F. Sift first 4 ingredients into medium bowl. Using electric mixer, beat butter and both sugars in large bowl until blended. Beat in eggs 1 at a time, then mashed bananas, sour cream, rum, and vanilla. Beat in dry ingredients in 2 additions just until combined. Spoon batter into pan.

Bake cake until tester inserted into center comes out clean, about 55 minutes. Cool 15 minutes.

Cut around cake.

Place platter over pan. Holding pan and platter together, turn over.

Let stand 5 minutes, then gently lift off pan. Cool at least 15 minutes for topping to set.

Serve warm or at room temperature with whipped cream or vanilla ice cream.