White Nectarine and Blackberry Upside-Down Cake

Any fresh stone fruits and berries can be used instead of nectarines.
Pineapple or pears can also be substituted. The one constant is the
lusciousness of the cake drenched in the caramelized juices and sugars
from the fruits.

If possible, bake this cake in a ten-inch cast-iron skillet, as you
can prepare the topping in the skillet, then add the cake, thereby
eliminating an extra pan. If you don’t have a cast-iron skillet,
substitute a nine-inch by three-inch round pan and increase baking
time by 10 to 15 minutes.

Ingredients:

Topping:

4 tablespoons unsalted butter (plus more if cake pan is used)
3/4 cup light brown sugar
4 nectarines
1 cup blackberries (or raspberries)
1 vanilla bean

Cake:

1 1/2 cups unbleached all-purpose flour
1 1/2 teaspoons baking powder
3 tablespoons cornmeal
pinch of salt
8 tablespoons unsalted butter, room temperature
1 cup plus 2 tablespoons granulated sugar
4 eggs at room temperature, separated
1 tablespoon pure vanilla extract
2/3 cup whole or 2% milk (soy or rice milk can be substituted)

Preparation:

Melt 4 tablespoons butter in a cast-iron skillet over medium heat, add
brown sugar and cook, stirring occasionally, for 3 to 4 minutes,
swirling pan to distribute evenly. Cut vanilla bean open and scrape
seeds into the mixture. Save bean for another use. Arrange fruit
slices in concentric circles in the pan, then sprinkle berries over
all, filling in any empty spaces.

Adjust oven rack to lower-middle position and heat oven to 350
degrees. Whisk flour, baking powder, cornmeal and salt in medium bowl.
Set aside.

Cream butter in a large bowl with an electric mixer using medium
speed. Gradually add 1 cup of sugar, beating until batter is light and
fluffy. Beat in yolks and vanilla, scraping down sides of the bowl
with a rubber spatula. Reduce speed to low and add dry mixture and
milk, alternately, in three or four batches, beginning and ending with
dry ingredients. Beat egg whites in a large bowl at low speed until
frothy. Increase speed to medium-high, beating to soft peaks.
Gradually add 2 tablespoons sugar and continue to beat to stiff peaks.

Fold one-quarter of beaten whites into batter with a rubber spatula to
lighten mixture. Fold in remaining whites until no white streaks
remain. Gently pour batter into pan and spread evenly on top of fruit,
being careful not to move fruit around.

Bake until top is golden and a toothpick inserted in the cake (not
fruit) comes out clean – about 45 to 50 minutes.

Place cake on cooling rack for about 2 minutes. Slide a paring knife
around the edge of the cake to loosen it. Then, using pot holders,
place a serving platter over the skillet tightly. Invert the cake onto
the platter. If any fruit sticks to the pan, remove it and position it
on top of the cake.

Serve warm with vanilla-whipped cream or vanilla ice cream.