Step 1: Prepare the Peaches

If using fresh peaches, blanch them in boiling water for 30 seconds, then transfer to an ice bath. The skins will slip off easily. Slice peaches into ½-inch wedges. If using frozen peaches, thaw completely and drain excess liquid.

Step 2: Create the Filling

In a large bowl, combine sliced peaches, both sugars, lemon juice, cinnamon, nutmeg, vanilla, cornstarch, and salt. Gently toss until peaches are evenly coated. Let the mixture sit for 15 minutes to draw out juices.

Step 3: Preheat and Prepare

Preheat your oven to 375°F (190°C). Place a 12-inch cast iron skillet in the oven while it preheats for 10 minutes to get hot.

Step 4: Make the Cobbler Topping

Whisk together flour, sugar, baking powder, and salt in a medium bowl. Using a pastry cutter or your fingertips, cut the cold butter into the dry ingredients until the mixture resembles coarse crumbs.

Step 5: Assemble and Bake

Carefully remove the hot skillet from the oven and add 2 tablespoons of butter, swirling to coat the bottom and sides. Pour in the peach mixture. Stir the boiling water into the flour mixture just until combined (it should be slightly lumpy). Drop spoonfuls of the batter evenly over the peaches. Sprinkle with coarse sugar if desired. Bake for 40-45 minutes until the top is golden brown and the filling is bubbling around the edges.