Preheat oven to 425°F and prepare a baking sheet with foil on the bottom rack.

In a large bowl, combine sliced peaches with lemon juice, sugars, cinnamon, nutmeg, and cornstarch. Mix well and pour into a baking dish.

Bake peach filling for 10 minutes while preparing the topping.

In a separate bowl, whisk together flour, sugars, baking powder, and salt. Add grated butter and toss to coat. Stir in boiling water until just combined with lumps.

Drop spoonfuls of topping over the baked peach filling. Sprinkle with additional cinnamon sugar if desired.

Bake until topping is golden brown, about 28 minutes. Serve warm or at room temperature.