Preheat the oven to 220 C / 425 F. Line your muffin tray cavities with paper liners.
Make the buttermilk - Combine milk and white vinegar in a bowl. Set aside for 5 minutes.You can also use store-bought buttermilk.
Sift the flour, baking powder, baking soda, and salt in a large bowl.
Whisk the buttermilk, oil, sugar, and vanilla extract in a separate bowl.
Pour the liquid mixture into the dry ingredients. Gently stir with a spatula, just until moistened.
Toss the chocolate chips with 1 teaspoon of flour and fold into the batter.
Divide the batter into the 12 muffin cavities and bake at 220 C / 425 F for 5 minutes. Then reduce the temperature to 190 C / 375 F for 12-15 minutes or until a skewer inserted in the center comes out clean.
Let cool in the pan for a few minutes before turning them out on a cooling rack.