Caramel Walnut Upside-Down Banana Cake

Oh, look what I went and did now. Really, I must be stopped–this is out of control. 







Caramel Walnut Upside-Down Banana Cake


If the caramel topping is still calling to you, despite my warnings that it is terrifically sweet and hardens once set, just be sure to serve it warm, before it does. A few other adjustments: the original recipe calls for an 8-inch cake pan, which is an absolute no-no. Mine completely filled a 9-inch pan with 2-inch sides. If you are nervous or don’t have at least 2-inch sides on your 9-inch baking pan, go for a 10-inch pan instead. Finally, I don’t know if my oven temperature is wonk or not, but this cake baked in 40 to 45 minutes in my oven, not 55+, something I have adjusted below.
Topping:
Nonstick vegetable oil spray
1/2 cup (1 stick) unsalted butter
1 cup (packed) golden brown sugar
3 tablespoons dark corn syrup
3/4 cup walnut halves or pieces
Cake:
1 3/4 cups cake flour
1 teaspoon baking powder
3/4 teaspoon baking soda
1/2 teaspoon salt
1/2 cup (1 stick) unsalted butter, room temperature
1/2 cup sugar
1/2 cup (packed) golden brown sugar
2 large eggs
1 cup mashed very ripe bananas (2 to 3 large)
3 tablespoons sour cream
1 tablespoon dark rum
1 teaspoon vanilla extract
Whipped cream or vanilla ice cream
For topping: Spray 9-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.
For cake: 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 40 to 45 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.