To Die For Blueberry Muffins

I didn't name this recipe, meaning, I wouldn't die for them, but they are very good muffins that taste like they came from a bakery. The recipe is the highest rated blueberry muffins on allrecipes.com, and I thought I'd given them a try. They were very, very good. I will definitely make them again.
Recipe courtesy Allrecipes

Serves 8 (Enough mixture for 12 muffin cup pan)

INGREDIENTS
1 1/2 cups all-purpose flour
3/4 cup white sugar
1/2 teaspoon salt
2 teaspoons baking powder
1/3 cup vegetable oil
1 egg
1/3 cup milk
(add): 1 teaspoon vanilla
1 cup fresh blueberries (or frozen, see below)
Topping:
1/2 cup white sugar
1/3 cup all-purpose flour
1/4 cup butter, cubed (at room temperature)
1 1/2 teaspoons ground cinnamon

DIRECTIONS
Preheat oven to 400 degrees F (200 degrees C). Grease muffin cups or line with muffin liners.

Combine 1 1/2 cups flour, 3/4 cup sugar, salt 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.

To Make Crumb Topping: Mix together 1/2 cup sugar, 1/3 cup flour, 1/4 cup butter, and 1 1/2 teaspoons cinnamon. Mix with fork, and sprinkle over muffins before baking.

Bake for 20 to 25 minutes in the preheated oven, or until done.

***This is what I did. I used frozen blueberries. I kept the blueberries in the freezer until I was done with making the mixture, and the struessel topping. I gently added in the frozen blueberries as the last step. Also, I baked them at 325 for 45 minutes, so that the blueberries did not sink the bottom too quickly, and made a nice round muffin top on the muffins.