I found a recipe on Allrecipes and substituted a couple of things to make it gluten and casein free and it was fantastic.   I used Namaste general purpose flour, but I am sure you could sub others.   

“Extra big blueberry muffins are topped with a sugary-cinnamon crumb mixture in this souped-up blueberry muffin recipe.”

Ingredients:
1 1/2 cups gluten free flour
3/4 cup white sugar
1/2 teaspoon salt
2 teaspoons baking powder
1/3 cup vegetable oil
1 egg
1/3 cup almond milk
1 cup fresh blueberries
1/2 cup white sugar
1/3 cup all-purpose flour
1/4 cup margarine, cubed
1 1/2 teaspoons ground cinnamon
Directions:
1. Preheat oven to 400 degrees F (200 degrees C). Grease muffin cups or line with muffin liners.
2. 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 almond 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.
3. To Make Crumb Topping: Mix together 1/2 cup sugar, 1/3 cup flour, 1/4 cup margarine, and 1 1/2 teaspoons cinnamon. Mix with fork, and sprinkle over muffins before baking.
4. Bake for 30 minutes in the preheated oven, or until done.