Combine the apples, brown sugar and cinnamon in a saucepan. Cook covered over medium heat about 5 minutes, until tender. Uncover and cook another 2–3 minutes to reduce the liquid, then set aside.

Put a 10-inch / 25 cm oven-safe skillet on the middle rack. Heat the conventional oven to 425°F / 220°C. Blend milk, eggs, sugar, flour, salt and xanthan into a completely smooth, thin batter. Rest 10–15 minutes while the pan heats.

Using oven mitts, remove the hot skillet. Add butter and swirl carefully to coat the base and sides. Immediately pour in the batter. Add half the cooked apples to the center, keeping the outer inch of batter clear.

Bake about 20 minutes without opening the oven, until the edges have risen and browned and the center is set and golden. Expect the pancake to settle after it leaves the oven.

Place the remaining apples in the center, dust lightly with powdered sugar and slice. Serve at once while warm.