Preheat oven to 200°C
Line 2 x 12 hole muffin tin with 18 paper liners
Sift Dry Ingredients: flour, baking powder, bicarb of soda, sugar and salt in a bowl.
Whisk Wet Ingredients: In a separate bowl, whisk buttermilk, melted butter, oil, eggs, vanilla and lemon zest.
Make a well in the dry mixture, pour in the wet mixture. Mix until just combined - try not to stir too much.
Stir through the 2 cups of blueberries - reserving the 1/2 cup for the topping.
Divide batter between paper liners and top with remaining blueberries.
Bake for 5 minutes, then turn oven down to 180°C and bake for a further 15 minutes or until a skewer inserted into the muffin comes out clean.
Remove muffins from the muffin tin immediately onto a cooling rack. Serve warm or at room temperature.