3 cups thinly sliced fresh peaches, about 6 to 8 peaches
1/2 cup each: white, brown sugar
1 cup plus 1 level tablespoon flour
1/2 teaspoon ground cinnamon
1/4 teaspoon ground mace
Zest from 1 lemon, optional
1 teaspoon baking powder
1/2 teaspoon salt
1/2 stick (1/4 cup) plus 2 tablespoons unsalted chilled butter, cut into small pieces
1/4 cup buttermilk
Heat oven to 425 degrees. Combine peaches, 1/4 cup each of white and brown sugar, flour, cinnamon, mace, zest, baking powder and salt in a large bowl, lightly tossing to coat peaches. Transfer to a 2-quart lightly buttered baking dish. Bake until peaches soften and release some juice, about 10 minutes.
Meanwhile, pulse together, flour, remaining 1/4 cup each white and brown sugars, baking powder and salt in a food processor. Pulse in butter until mixture resembles coarse meal. Slowly pour in buttermilk, pulsing until mixture just comes together in a ball. Remove from food processor.
Remove peaches from oven. Press together strips of dough and top peaches in pan, working in a lattice pattern if dough allows or flatting dough into square pieces and topping peaches, arranging as desired. Bake until topping is golden about 30 minutes. Transfer to a rack to cool, about 25 minutes.