Source – Williams-Sonoma
For the topping:
1/4 cup (1½ oz/ 45g) all-purpose (plain) flour
2 tablespoons each granulated sugar and firmly packed light brown sugar
1/4 teaspoon ground cinnamon
2 tablespoons cold unsalted butter, cut into small pieces.
For the muffins:
7 tablespoons (3½ oz/ 105g) unsalted butter, at room temperature
3/4 cup (6oz/185g) granulated sugar
2 large eggs
2 & 1/4 cups (11½ oz/ 360g) all-purpose (plain)flour
4 teaspoons baking powder
1/2 teaspoon salt
1 cup (8 fl oz/ 250ml) milk
1 & 1/2 teaspoons vanilla extract (essence)
1 & 1/2 cups (6 oz/ 185g) fresh blueberries or frozen unsweetened blueberries, unthawed.
Preheat the oven to 375 Fahrenheit (190 degree celcius) . Grease 12 standard muffin cups with butter or butter-flavoured nonstick cooking spray
To make the topping, stir together the flour, granulated sugar, brown sugar, and cinnamon in a small bowl. Using a pastry cutter or your fingers, cut or rub the butter into the dry ingredients just until coarse crumbs form. Alternatively, combine the dry ingredients and the butter in a food processor and pulse just until coarse crumbs form.
To make the muffins, in a bowl, using an electric mixer on medium speed, cream together the butter and sugar until light and fluffy. Add the eggs, one at a time, beating well after each edition until blended into the butter mixture.
In another bowl, stir together the flour, baking powder, and salt. Add the dry ingredients to the butter mixture in 2 increments, alternating with the milk and vanilla. Stir just until evenly moistened. The batter will be slightly lumpy. Using a large rubber spatula, gently fold in the blueberries just until evenly distributed, no more than a few strokes. Take care not to break up the fruit. Do not overmix.
Spoon the batter into each muffin cup, filling it level with the rim of the cup. Sprinkle each muffin with some topping.
Bake until golden, dry, and springy to the touch, 20-25 minutes. A toothpick inserted into the center of a muffin should come out clean. Transfer the pan to a wire rack and let cool for 5 minutes. Unmold the muffins. Serve warm or at room temperature.