Amazing Blueberry Muffins - my dad's recipe

Steve's Blueberry Muffins
1 ½ cups all-purpose flour
¾ cup white sugar
½ teaspoon salt
2 teaspoons baking powder
1/3 cup vegetable oil
2 TBS of finely grated lemon peel
1 egg
1 cup fresh blueberries

Crumble:
½ cup white sugar
1/3 cup all-purpose flour
¼ cup butter, cubed
1 ½ teaspoons ground cinnamon

Preheat oven to 400 degrees. Grease muffin tins with Crisco or line with muffin liners. Combine 1 ½ cups flour, ¾ cup sugar, salt, lemon peel, and baking powder. Place 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 muffin cups right to the top, and sprinkle with crumb topping mixture. Mix the crumble ingredients with a fork before sprinkling on top of muffin mixture. Bake for 20-25 mins. Yield: 12 muffins