Blueberry Coffee Cake Muffins

This is a very old and really good recipe.
I've been making this blueberry cake for years.
It works well as either a coffee cake or muffins.

Ingredients:
2 cups all-purpose flour
2 teaspoons baking powder
1/2 teaspoon salt
1/4 cup vegetable oil
3/4 cup white sugar
1 egg
1/2 cup milk
1 cup blueberries
1/3 cup all-purpose flour
1/2 cup white sugar
1/2 teaspoon ground cinnamon
1/4 cup butter, softened

Directions:
For the topping:
In a bowl, combine 1/3 cup flour, cinnamon and 1/2 cup sugar.
Cut in the butter until mixture resembles coarse crumbs.

Directions:
For the cake:
Preheat oven to 375 degrees F.
Grease and flour a 9 inch pan. Sift together the flour,
baking powder and salt. Set aside.
In a large bowl, whisk together the oil, sugar and egg.
Stir in the flour mixture alternately with the milk,
mixing just until incorporated. Fold in the blueberries.
Pour batter into prepared pan. Cover with streusel topping.

Bake for 45 minutes, or until a toothpick inserted
into the center of the cake comes out clean. Allow to cool.