For me the perfect blueberry muffin is light, fluffy and bursting with blueberries. I add a touch of ginger because it perks up the flavor of the berries, but not so much that it's overpowering. The topping is buttery, sweet and bakes into a lacy crust. I like to bake them in large "Texas-sized" muffin cups, so there is lots of muffin top and just as much of the berry center. (They are great small, but I am always left wanting more and for some reason, I feel less guilty eating one big one, instead of two little ones. )
Prepare a muffin pan with 6 giant muffin cups or 12 normal sized papers.
In a large bowl whisk together the self-raising flour and nutmeg. In a separate bowl combine the melted butter, sugar, egg, milk, vanilla and ginger. Gently stir the wet into the dry ingredients only until combined. Gently fold in the blueberries. If using frozen berries, do this in as few stirs as possible or the batter will turn purple.
Divide the batter into the prepared muffin cups.
To make the topping:
Quickly mix the butter into the flour mixture, which will break up the butter slightly, but it should still stay cold. If the butter warms up too much, stick the bowl in the freezer for about 5 minutes.
Divide the topping over the muffins.
Bake for about 30 minutes (about 20 minutes if using the smaller cups), or when golden on top and a tester comes out clean.
Allow to cool on a rack for 5 minutes.
Serve warm or room temperature.