The quince is not edible until cooked, when it becomes soft and tender. Its flavor blends nicely with this pound cake.
Heat oven to 325 degrees. Position rack in center of oven. Coat two 8-inch-square baking pans with cooking spray, and line bottoms with parchment paper. Set aside.
In a large bowl, sift together the flour and baking powder. Set aside.
Place the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment, and beat on medium speed until fluffy, about 2 minutes. Reduce mixer speed to low, and add the egg yolks one at a time, alternating with about 1/4 cup of the flour mixture each addition.
Increase mixer speed to medium, and add the vanilla and cream; the batter will become thick. Transfer the batter to a large mixing bowl.
Place the egg whites in the clean bowl of the electric mixer fitted with the whisk attachment. Beat egg whites on medium-high speed until stiff peaks form, about 2 minutes. Using a rubber spatula, stir about one-quarter of the egg whites into the batter. Fold in the remaining egg whites.
Spoon batter into prepared pans. Run a knife through batter to remove any air bubbles. Bake until a cake tester inserted into the middles comes out clean, 60 to 70 minutes. Transfer to a wire rack to cool, 1 to 1 1/2 hours. Turn out cakes, and wrap in plastic; let cakes sit overnight.
Trim cakes with a serrated knife so the tops are level. Using a 2-inch-round cookie cutter, cut each cake into 10 circles.
When ready to serve, toast the pound cakes under a broiler until golden, about 1 minute. Serve with a scoop of quince sorbet and 3 slices of poached quince.
Quinces, the fruit of love, are available at many supermarkets from fall through early winter.