Place the chestnuts in a large bowl and cover completely with water. Soak for at least 30 minutes, or up to 1 hour, then drain and pat dry.
Preheat the oven to 400F. Using a small sharp knife, carefully score an “X” across the rounded side of each chestnut, cutting through the shell but not too deeply into the nut. To do this, I like taking a mason jar lid, placing the chestnut shell side up on the inside, and cutting down to avoid slicing entirely through the nut.
Arrange the scored chestnuts cut-side up on a rimmed sheet pan in a single layer. Roast for 35 to 40 minutes, shaking the pan once halfway through, until the shells have curled back and the chestnuts are tender and lightly golden.
Remove from the oven, wrap the hot chestnuts in a clean kitchen towel or paper bag, and let them steam for 5 minutes. Peel while still warm, discarding both the hard shell and the thin inner skin, and serve immediately.