This recipe for soft, chewy muffins makes 12 regular-sized muffins or 8 jumbo muffins.
The muffins will keep in an airtight container for up to 3 days.
Preheat the oven to 375 ºF (190 ºC) and line a muffin tin with paper liners.
For the streusel topping, stir the flour, brown sugar, baking powder and cinnamon together in a small bowl. Work in the butter with your fingertips until the mixture is roughly crumbled and no large pieces of butter are visible. Set aside.
In a large mixing bowl, beat the butter, sugar and lemon zest together, until well combined. Add the eggs one at a time, mixing well after each addition.
In a separate bowl, sift the flour, baking powder, salt and nutmeg. Add half of this to the butter mixture and stir until blended. Add the milk, stir well and then stir in the remaining flour until smooth. Gently stir in the blueberries.
Scoop the batter into the prepared muffin tin (they will fill right to the top of the muffin cups) and sprinkle the streusel mixture overtop. Bake the muffins for about 35 minutes, until a tester inserted in the centre of a muffin comes out clean. Cool the muffins in the tin for 15 minutes, then turn out onto a cooling rack to cool completely.