Blood Orange Polenta Upside-Down Cake with Whipped Crème Fraîche

To make the cake

Position rack in center of oven and preheat to 350° F.

Combine 6 tablespoons sugar and water in a 10-inch-diameter ovenproof skillet with 8-inch-diameter bottom and 2 1/2-inch-high sides. Stir over medium heat until sugar dissolves. Increase heat and boil without stirring until syrup is golden amber (not dark amber), occasionally brushing down sides of skillet, about 4 minutes. Remove skillet from heat and whisk 2 tablespoons butter into caramel. Set aside.

Cut off both rounded ends of each orange so that ends are even and flat. Using a sharp knife, cut oranges into 18-inch-thick rounds. Remove and discard any seeds. Arrange orange slices, overlapping slightly, in concentric circles atop caramel in bottom of skillet.

Whisk flour, polenta, baking powder and coarse salt in a medium bowl to blend. Using an electric mixer, beat 3/4 cup sugar, remaining 6 tablespoons room-temperature butter and vanilla in another medium bowl until light and fluffy. Add egg yolks one at a time, beating well after each addition. Add flour mixture in three additions alternately with milk in two additions, beating batter just until incorporated.

Using clean, dry beaters, beat egg whites in a large bowl until soft peaks form. Add remaining 1 tablespoon sugar and beat until stiff but not dry. Fold 1/3 of egg whites into batter to lighten, then fold in remaining egg whites in two additions. Drop batter by large spoonfuls atop orange slices in skillet, then spread evenly.

Bake cake until tester inserted into center comes out clean, about 45 minutes. Cool cake in skillet for 10 minutes. Run a small knife around cake to loosen. Place on platter atop skillet. Using oven mitts, hold platter and skillet firmly together and invert, allowing cake to settle onto platter. Rearrange any orange slices that may have come off. Cool cake completely at room temperature.

For whipped crème fraîche

Using an electric mixer or beaters, beat chilled crème fraîche and 2 tablespoons sugar in a medium bowl until mixture thickens. If using whipping cream, beat with sugar until soft peaks form.

Cut cake into wedges and serve with dollop of whipped crème fraîche.