Peel the sweet potatoes and slice them approximately ¼-inch thick. Thin slices cook evenly and absorb the buttery syrup.

Heat the oven to 375°F and lightly butter a 9 × 13-inch baking dish. Place the dish on a foil-lined sheet pan to catch any bubbling syrup.

Add the sweet potatoes, granulated sugar, brown sugar, water, butter, cinnamon, nutmeg, and salt to a saucepan. Bring the mixture to a gentle simmer and cook for 8–10 minutes, until the butter melts and the syrup smells fragrant while the potatoes remain firm.

Remove the saucepan from the heat and stir in the vanilla extract. Allow the mixture to cool briefly while you prepare the crust.

Fit one pie crust into the buttered baking dish, trimming or folding the edges as needed. Pour the sweet potatoes and all of the syrup into the crust.

Cover the filling with the second pie crust and seal or crimp the edges. Cut several vents in the top, brush with melted butter, and sprinkle with the optional tablespoon of sugar.

Bake for 45–55 minutes, until the crust is deep golden brown and the filling bubbles around the edges. Loosely cover the cobbler with foil if the crust begins to brown too quickly.

Let the cobbler rest for at least 15–20 minutes before serving. The syrup thickens as it cools, making each portion easier to spoon and serve.