Heat the oven to 350°F with a rack in the center. Have a 12-inch cast-iron skillet or a 13x9-inch baking dish ready.

Put the sliced peaches in a large bowl with the brown sugar, 1/4 teaspoon salt, lemon juice, 1 teaspoon vanilla, 1 teaspoon cinnamon, nutmeg, and bourbon if you like. Stir gently and let sit at room temperature for 15 to 30 minutes so the fruit releases its juices. If the peaches are very ripe and loose, skip this rest, lift the peaches out with a slotted spoon when assembling, and simmer the extra juices in a small saucepan for 5 to 10 minutes to make a light syrup for drizzling.

Mix the granulated sugar with the reserved lemon zest in a medium bowl. Rub the zest into the sugar with your fingertips until the sugar looks like wet sand and smells strongly of lemon.

Whisk the flour, baking powder, remaining 3/4 teaspoon salt, cinnamon, and the lemon sugar into the same bowl until they are evenly blended.

Make a well in the center of the dry ingredients, then pour in the buttermilk and remaining 1 teaspoon vanilla. Stir just until the batter comes together and only a few lumps remain. To make quick buttermilk, put 2 1/2 tablespoons of white vinegar or lemon juice in a 2-cup measuring cup, add milk to the 1 1/2-cup line, and let it sit for 7 to 10 minutes before using.

Place the butter in the skillet or baking dish and set the pan in the oven just until melted, 4 to 5 minutes. Remove the hot pan and tilt it so the butter coats the bottom evenly. If making a half batch, use a 9x9-inch or 8x8-inch pan.

Pour the batter over the melted butter and spread it gently without stirring it into the butter. Spoon the macerated peaches and any juices evenly over the batter. Bake for 45 to 50 minutes, until the top is puffed and golden brown and the filling is bubbly around the edges. A half batch will likely bake faster, while a taller 2-quart dish may need more time.

Cool the cobbler on a wire rack for 15 to 30 minutes before serving. Serve warm with vanilla ice cream.