Preheat your oven to 190°C (375°F) and lightly grease a 23 x 33 cm baking dish with butter.
In a large bowl, combine the sliced peaches, 100 g granulated sugar, brown sugar, cornstarch, lemon juice, 5 ml vanilla, cinnamon, and nutmeg; toss until evenly coated.
Poured the peach mixture into the prepared baking dish and dot with half of the cubed butter.
In a separate bowl, whisk together the flour, 80 g granulated sugar, baking powder, and salt.
Cut the remaining butter into the flour mixture until it resembles coarse crumbs.
Stir in the milk and remaining 5 ml vanilla extract until just combined to form a shaggy dough.
Drop the dough in rustic spoonfuls over the peach filling.
Sprinkle the top with the coarse sugar.
Bake for 45 minutes, or until the fruit is bubbling and the topping is golden brown.
Let cool for 10 minutes before serving.