Combine the sliced peaches with granulated sugar, light brown sugar, ground cinnamon, ground nutmeg, lemon juice, cornstarch, and vanilla extract. Let sit for 10-15 minutes.

Preheat oven to 350°F and warm the skillet for 5 minutes.

Whisk together flour, granulated sugar, light brown sugar, baking powder, and salt. Cut in the chilled butter until coarse crumbs form.

Stir in boiling water until just combined. Rest briefly.

Melt 3 tablespoons of butter in the hot skillet.

Pour the peach mixture into the skillet and spread evenly.

Dollop spoonfuls of topping over the peaches, leaving some visible.

Optional: sprinkle coarse sugar over the topping.

Bake for 40-45 minutes until golden-brown and bubbly.

Let cool for a few minutes before serving warm.