Preheat the oven to 200C/180C Fan/Gas 6 and grease a 10–12-hole muffin tin.

Mix the oat milk and vinegar together and leave for about 5 minutes to create a buttermilk-like consistency.

Sift all the dry ingredients together in a large bowl. Pour the remaining wet ingredients into the milk and vinegar and whisk together. Fold the wet ingredients into the dry, making sure no pockets of flour have been left.

Add half the frozen blueberries, if using, to the mixed batter and turn gently (you just want to fold them in to prevent the colours mixing). Divide the mixture evenly between the muffin tin holes and top each one with a few of the remaining frozen berries , nuts and oats and push into the surface. Bake for 25–30 minutes until a skewer inserted into the centres comes out clean. Remove from the tin and allow to cool completely.