Preheat oven to 425°F.
In a large bowl, stir the peaches, brown sugar, sugar, corn starch, vanilla, lemon juice, cinnamon, and nutmeg together. Pour the mixture into a 2-quart (8x8-inch) baking pan.
9 fresh peaches, ½ cup brown sugar, ½ cup granulated sugar, 2 teaspoons cornstarch, 2 teaspoons pure vanilla extract, 1 teaspoon fresh lemon juice, ½ teaspoon ground cinnamon, 1 pinch ground nutmeg
Cover the pan with aluminum foil and bake for 10 minutes.
While the filling bakes, make the topping: In a medium bowl, whisk the flour, sugars, baking powder, cinnamon, and salt together. Add in the butter and pinch the butter into the flour mixture until the butter pieces are pea-size. Pour in the boiling water and stir just until it starts to come together but still leaving chuncks.
2 cups all-purpose flour, ½ cup brown sugar, ½ cup granulated sugar, 2 teaspoons baking powder, 2 teaspoons ground cinnamon, ½ cup unsalted butter, ½ teaspoon kosher salt, ¼ cup boiling water
Once baked, remove the filling mixture from the oven. Spoon the crumble mixture over the filling and return it to the oven.
Bake for 30-35 minutes, until the topping is golden brown.
Let cool for at least 15 minutes before serving.