Preheat Oven: Set oven to 425°F (220°C) and place a 10-inch oven-safe skillet or cast-iron pan inside to heat.
Blend Batter: In a blender, combine eggs, milk, gluten-free flour, sugar (if using), vanilla, and salt. Blend until smooth, about 30 seconds. Let the batter rest for 5 minutes.
Heat Butter: Carefully remove the hot pan from the oven. Add butter and swirl to coat the bottom and sides.
Bake: Pour the batter into the hot skillet and immediately return it to the oven. Bake for 15–17 minutes, until the pancake is puffed and golden brown.
Serve: Dust with powdered sugar and top with fresh fruit if desired. Serve immediately — it will deflate as it cools.