Preheat the oven to 180C/356F. Either grease or line your muffin tin with 6-7 liners. For whatever reason, I find that muffin liners result in muffins with a more rounded muffin top that doesn't spill out so much, but both options work well.

Combine the flours, baking powder, baking soda, xanthan gum and salt in a medium mixing bowl and whisk to combine.

In a large mixing bowl, combine the oil, butter, sugars and egg.

Use a hand beater or stand beater to beat the mixture for 1-2 minutes or until lighter and foamy. The butter should have incorporated completely into the mixture, with no chunks remaining.

Turn the beaters to low and alternate between adding the flour mix and milk. Continue until you have used up all the flour and milk.

Add your add ins and vanilla bean paste (if you are using them) to the batter and stir gently to just combine. Pour the batter into the prepared muffin holes, then garnish with the reserved add ins if using. I also like to finish mine with sanding sugar or finishing sugar for a crunchy top, but this is optional.

Bake for 20-25 minutes or until golden brown and cooked through.

Allow to cool for 5-10 minutes before removing from the tin. Cool on a wire rack and serve.