
In a small bowl, combine gluten-free flour, baking powder, xanthan gum (if needed), baking soda, cinnamon, and salt. Whisk to combine. Set aside for now.
In a large bowl, whisk together sugar, sour cream, eggs, melted butter, vegetable oil, and vanilla extract. Whisk until well combined.
Add the dry ingredients to the wet ingredients. Stir until no lumps of dry flour remain. Do not overmix.
Gently stir the chocolate chips into the muffin batter.
In a 12-cup, paper wrapper-lined muffin tray, evenly scoop the muffin batter into the 12 paper liners. They should each be about ¾ cups full.
Let the muffin batter rest here for 15 minutes before baking. This gives the gluten-free flour a chance to absorb some of the liquid ingredients.
Preheat the oven to 350°F (177°C).
Bake the muffins for 20 to 22 minutes or until lightly browned and cooked throughout. To test, insert a toothpick into the baked muffin. If no wet batter remains on the toothpick, the muffins are done baking.
Let the muffins cool slightly before removing them from the tray.