Makes 9 servings
Hands-on time: about 15 minutes
Total preparation time: about 55 minutes
8 tablespoons (1 stick) unsalted butter, softened
3 tablespoons light brown sugar
1 tablespoon plus 1 teaspoon vanilla extract
2 medium nectarines, each cut into 8 slices
2 large plums, each cut into 8 slices
2/3 cup granulated sugar
2 large eggs
1 1/2 cups cake flour
2 teaspoons ground cinnamon
1 3/4 teaspoons baking powder
1/2 teaspoon table salt
1/4 teaspoon ground nutmeg
1/4 cup milk
Preheat the oven to 350°F. Combine 2 tablespoons of the softened butter, the brown sugar, and 1 teaspoon vanilla in a small bowl. Lightly grease the sides of an 8-inch square cake pan; spread the brown-sugar mixture evenly over the bottom of the pan. Arrange the nectarine and plum slices in alternate rows over the brown-sugar mixture in the pan.
Combine the granulated sugar and the remaining 6 tablespoons butter in the bowl of a food processor fitted with a chopping blade. Process until fluffy, about 1 minute. Add the eggs and 1 tablespoon vanilla and process until combined. Add the flour mixed with the cinnamon, baking powder, salt, and nutmeg; pour the milk over all. Pulse once or twice, just until the flour is moistened. The batter doesn’t have to be smooth.
Spoon the batter evenly over the fruit in the pan and bake until the center springs back when gently pressed, about 40 minutes. Cool on a rack in the pan for 5 minutes, then loosen the edges and invert onto a serving plate. Cut into squares and serve warm.