Whisk together gluten-free flour, sugar, baking powder, and salt in a medium bowl.
In a small bowl, whisk milk, egg, melted butter, and vanilla extract until combined.
Pour wet ingredients into dry ingredients and whisk until smooth. Let the batter rest for 5-10 minutes.
Preheat a cast iron skillet or electric griddle to medium heat, and grease with nonstick spray or melted butter.
Scoop 1/4 cup batter onto the hot surface. Cook until bubbles form and pop, then flip and cook until golden brown.
Serve immediately or keep warm in the oven at 100-200 degrees for up to 20 minutes.
For sheet pan pancakes, preheat oven to 350 degrees, line a quarter sheet pan with parchment paper, pour in batter, and bake for 15-17 minutes. Slice into squares and serve