Preheat the oven to 180C/356F. Either grease or line your muffin tin with 8-10 liners.
Combine the flours, almond meal, baking powder and baking soda in a medium mixing bowl and whisk to combine.
In a large mixing bowl, combine the oil, butter, sugar 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 the chopped feijoa and white chocolate chips to the batter and stir gently to just combine. Pour the batter into the prepared muffin holes, then garnish with the reserved feijoa and white chocolate chips.
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.