American
Heat the oven to 200C and line 8 cups of a muffin tin with paper cases.
For the topping, rub 40 g of the flour, 100 g of the sugar, 55 g of cold butter and the cinnamon together with your fingertips until crumbly.
In a large bowl, whisk the remaining 190 g flour and 150 g sugar with the baking powder and salt.
Melt the remaining 90 g butter, whisk it with the egg and milk, pour into the dry ingredients and stir just until combined.
Gently fold in the blueberries and divide the batter among the cases, filling them almost to the top.
Sprinkle with the crumb topping and bake for 20-25 minutes until a skewer inserted in the center comes out clean.
Cool in the tin for 5 minutes, then move the muffins to a rack.