In a large bowl, fold the peaches, 1/4 cup each of white and brown sugars, cinnamon (1/4 teaspoon), nutmeg (1/8 teaspoon), lemon juice (1 teaspoon), and cornstarch (2 teaspoons) until all ingredients are well combined.
Pour fruit mixture into a 9X13-inch baking dish.
Place in the preheated oven and bake for 10 minutes.
While peaches are in the oven, mix together all the cake topping ingredients, except the boiling water to a medium bowl.
Use a pastry blender to cut the butter into the dry ingredients (12 tablespoons) until the mixture looks like a coarse meal.
Pour in the boiling water (1/2 cup) and stir just until the mixture comes together and is just mixed through.
After the peaches have baked the 10 minutes, pull them from the oven and drop large spoonfuls of the dough topping over the peaches.
Evenly sprinkle the top of the dough with the 3 tablespoons of sugar.
Place the baking dish on a rimmed baking sheet in case the cobbler bubbles over and drips, and bake for 30 minutes or until the topping is golden and baked through and the peaches are tender.
Notes
Taste your peaches first: This lets you adjust the sugar based on how sweet or tart your peaches are.
Don’t skip the initial bake: That first bake gives the peaches a head start so they soften, release their juices, and turn syrupy instead of watery. It also helps create that jammy, old-fashioned cobbler filling.
Cut in the cold butter: Those little pieces of cold butter melt as the topping bakes, creating a tender, buttery texture with lightly crisp edges. Don’t overmix it into a paste.
Drop the topping evenly: Spoon the topping over the peaches in fairly even portions so it bakes consistently and gives you that classic cobbler texture.
Bake until bubbling, not just golden: A golden topping is only part of the doneness cue. The filling should be bubbling thickly around the edges so you know it has fully cooked and thickened.
Let it rest before serving: Give the cobbler a little time to cool so the filling can set into that rich, scoopable texture.