Plum-Nectarine Buckle

1 . Stage

Preheat oven to 350 degrees F. Brush a 9-inch square cake pan or 10-inch cast iron skillet with 2 tablespoons butter; set aside. Whisk together flour, 3/4 cup sugar, the baking powder, allspice, and salt in a medium bowl; set aside.

2 . Stage

Whisk together egg, milk, vanilla, and remaining 4 tablespoons butter in another medium bowl. Add egg mixture to flour mixture; stir to combine. Spread batter evenly into buttered pan.

3 . Stage

Toss plums, nectarines, lemon juice, remaining 1/4 cup plus 2 tablespoons sugar, and a pinch of salt in a large bowl. Spread fruit mixture evenly over batter. Sprinkle with topping. Bake until a cake tester inserted into center comes out with moist crumbs, about 1 hour and 15 minutes. Let cool in pan on a wire rack 1 hour before serving.

4 . Stage

To prepare crumble topping: Put butter and brown sugar, and orange zest if desired, in the bowl of an electric mixer fitted with the paddle attachment. Mix on medium speed until creamy. Stir in flour and salt. Work mixture through fingers until it forms coarse crumbs ranging in size from peas to gum balls.