To make the topping, mix together 1/2 cup sugar, 1/3 cup flour, and 1/4 cup butter, and 1 1/2 teaspoons cinnamon, mix with a fork, and sprinkle over the muffins before baking.
Preheat the oven to 400F, 200?c, Gasmark 6; grease the muffin cups or line with muffin liners.
Combine 11/2 cups flour, 3/4 cup sugar, salt and baking powder, place the vegetable oil into a 1 cup measuring cup; add the egg and enough milk to fill the cup.
Mix this with flour mixture fold in blueberries fill the muffin cups right to the top, and sprinkle with crumb topping mixture.
Bake for 20 to 25 minutes in the preheated oven, or until done.
Fresh fruit introduces excess moisture into standard batter formulas, which alters the crumb structure if handled incorrectly. Using fresh blueberries requires gentle folding to prevent the anthocyanin pigments from bleeding into the batter and turning the crumb grey. Frozen berries, by contrast, release even more water upon thawing and must remain frozen solid when incorporated to maintain structural integrity. Dividing the liquid components into a standard measuring cup ensures the exact ratio of egg and milk integrates smoothly with the oil without overworking the gluten. Baking at 400°F provides the initial thermal shock needed to rapidly activate the baking powder, producing the characteristic high-domed top associated with commercial bakery goods. Extending batter fills right to the rim of each muffin cup forces the rising structure upward rather than outward. Quantities in this formulation scale linearly, meaning operators can double the dry and wet components proportionally without altering the 20 to 25 minute bake time, provided individual pan cavities remain standard size.