Heat oven to 180C/160C fan/gas 4. Place the muffin cases in a muffin tray. In a large bowl, combine the flour, baking powder, bicarb, sugar and 1/2 tsp salt. Whisk the butter, buttermilk, eggs, maple syrup and vanilla extract in a jug. Pour the wet ingredients into the dry and add most of the blueberries. Stir briefly to just combine, but don’t overmix or the muffins will be heavy.