These blueberry crumb cake muffins are a delicious and easy-to-make treat. The muffin batter is made in a food processor, with flour, sugar, baking powder, salt, butter, eggs, and milk. The blueberries are folded into the batter and the streusel topping is made with flour, sugar, butter, and cinnamon, mixed in the food processor until it forms coarse crumbs. The muffins are baked until golden brown and the streusel is crunchy. These muffins are perfect for breakfast or a snack.