Apple Pie Muffins

I was making muffins, and the idea of apple pie muffins came to mind. I adapted this recipe from here. These were delicious.

Crumb topping:
1/4 cup  firmly packed  brown sugar
1/3 cup all-purpose flour
1/4 cup unsalted butter, softened
1 teaspoon cinnamon

Muffins:
3/4 - 1 cups firmly packed brown sugar
1/2 cup canola oil
1 egg
1 1/2 teaspoons vanilla
1-2 teaspoon cinnamon
2 1/2 cups all-purpose flour (I used 2 cups white whole wheat/1/2 cup white)
1 teaspoon baking soda
1/4 teaspoon salt
1 cup buttermilk (I used 1 tsp. apple cider vinegar and milk to make 1 cup)
3 cups diced peeled firm tart apples (I tossed mine with 1 tsp. cinnamon & 1 tsp brown sugar)

Topping: In a small bowl toss together sugar, flour, butter and cinnamon until crumbly; set aside. Muffins: In a large bowl whisk together brown sugar, oil, egg, cinnamon, and vanilla until smooth. In a separate bowl, sift together flour, soda and salt. Mix in dry ingredients, then add buttermilk. Fold in apples, mixing just until combined. Spoon into greased muffin cups filling 3/4 full.
Sprinkle topping over evenly.  Bake at 400°F for 15-20 minutes.