Lightly grease the insert of a 5- to 6-quart slow cooker with butter or nonstick spray to prevent sticking and make cleanup easier.
butter or nonstick spray
In a large bowl, combine the sliced peaches, 1/3 cup granulated sugar, 1/4 cup packed light brown sugar, cornstarch, lemon juice, 1 teaspoon cinnamon, nutmeg (if using), 1 1/2 teaspoons vanilla, and a pinch of salt. Gently toss until the peaches are well coated and no dry cornstarch remains.
6 cups peaches, 1/3 cup granulated sugar, 1/4 cup light brown sugar, 2 tablespoons cornstarch, 1 tablespoon lemon juice, 1 teaspoon ground cinnamon, 1/4 teaspoon ground nutmeg, 1 1/2 teaspoons vanilla extract, salt
Pour the peach mixture into the prepared slow cooker and spread it into an even layer so the fruit is distributed evenly.
6 cups peaches
In a medium bowl, whisk together the flour, 3/4 cup granulated sugar, baking powder, 1/4 teaspoon salt, and 1/2 teaspoon cinnamon (if using). In a separate bowl or measuring cup, mix the melted butter, milk, and 1 teaspoon vanilla. Pour the wet ingredients into the dry and stir just until a thick, pourable batter forms; do not overmix.
1 cup all-purpose flour, 3/4 cup granulated sugar, 1 1/2 teaspoons baking powder, 1/4 teaspoon salt, 1/2 teaspoon ground cinnamon, 1/2 cup unsalted butter, 1/2 cup milk, 1 teaspoon vanilla extract
Spoon or pour the batter evenly over the peaches in the slow cooker. It does not need to be perfect; the batter will spread as it cooks, and a few exposed peach slices are fine.
Cover the slow cooker with the lid. Cook on HIGH for 2 1/2–3 hours or on LOW for 5–6 hours, until the peaches are bubbling around the edges and the topping is set in the center and springs back lightly when pressed.
For the last 20–30 minutes of cooking, prop the lid open slightly with a wooden spoon or folded kitchen towel to let steam escape and help the topping firm up.
Turn off the slow cooker and let the cobbler rest, uncovered, for 15–20 minutes to allow the juices to thicken slightly and make serving easier.
Spoon the warm peach cobbler into bowls. Top with vanilla ice cream, whipped cream, and a light sprinkle of cinnamon if desired.
vanilla ice cream, whipped cream, ground cinnamon