Preheat the oven to 220C fan forced (or 425F) and generously grease a 12 cup muffin baking pan with butter or oil.
In a large bowl, sift the flour, baking powder, baking soda and salt together and whisk well to combine. Set aside.
In a medium bowl, combine the melted butter with the sugar and lemon zest and whisk well. Add the eggs, milk and lemon juice mixture and vanilla and mix again.
Take 1 tablespoon of the dry mixture and place in a smaller bowl and stir through blueberries until the berries are well coated in the flour mixture (this helps evenly distribute the berries throughout the mixture and prevents them from sinking to the bottom of the muffins).
Make a well in the centre of the dry mixture and add the wet ingredients. Gently fold the mixture until just combined (about 9 folds) and then gently fold the berries in until just incorporated.
Evenly divide the batter into the 12 muffin cups, making sure that the mixture is topped to the brim (tip: using an ice cream scoop can help ensure even amounts of mixture in each muffin cup).
Bake for 5 minutes at 220C (425F), then reduce the heat to 190C (375F) and bake for another 15 minutes or until a toothpick inserted into the centre comes out clean.
Muffins will keep up to 3-4 days in an airtight container -simply reheat in oven or microwave and top with a knob of butter (for extra buttery deliciousness, of course).