Preheat your oven to 375°F (190°C).
Line the muffin tin with paper liners or grease it lightly.
In a large mixing bowl, combine the gluten-free flour, baking powder, salt, and sugar. Whisk well.
In a separate bowl, beat the egg and mix in the milk, oil, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir gently until just combined.
Fill each muffin cup about two-thirds full with the batter.
Bake in the preheated oven for 18-20 minutes, or until a toothpick comes out clean.
Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.