Eggy, your blueberry muffin recipe sounds delicious. This is a topping I frequently use for blueberry muffins. It is easy to make and makes the muffins look very attractive. I don't have any particular measurements, it's just a "dump it together" kind of recipe.

Combine about 3 tablespoons white granulated sugar and the finely grated rind from 1 small lemon (only the yellow part of the rind). Rub the sugar and grated rind together, then sprinkle on top of the muffin batter in each individual muffin cup.