Preheat oven to 400°F. Butter and lightly flour 10-inch-diameter springform pan, tapping out any excess flour. Line bottom of pan with parchment; grease parchment with butter.

Sift flour, baking powder, baking soda, and salt into a bowl. In another large bowl, whisk 3⁄4 cup sugar, 6 tablespoons butter and 3 tablespoons olive oil until smooth. Whisk in eggs, both peels and vanilla. Add flour mixture alternately with wine in 3 additions each, whisking after each addition just until smooth. Transfer batter to prepared pan and smooth out the top. Place grapes over batter.

Bake cake for 20 minutes, then remove from oven. Dot top of cake with 2 tablespoons butter, then sprinkle 2 tablespoons sugar over it. Return cake to oven; bake until golden and tester inserted into center comes out clean, about 20 minutes more. Cool in pan on a wire rack 20 minutes. Use a knife to trace the edge of the cake before releasing pan sides. Serve slightly warm or at room temperature.