Whole Wheat Huckleberry Crumb Muffins

Preheat oven to 350 degrees F (175 degrees C). Spray 1 muffin tin with cooking spray.

Combine milk, sugar, butter, egg, and vanilla extract in a bowl; mix until completely combined.

Whisk all-purpose flour, 1/2 cup plus 1 tablespoon whole wheat flour, baking powder, and salt in a separate bowl; fold into the milk mixture until batter is just combined. Fold in huckleberries to distribute them evenly.

Pour batter into the greased muffin tin.

Combine the remaining 1/4 cup whole wheat flour, oats, brown sugar, cold butter, and cinnamon in a bowl. Mix until crumbly and sprinkle over the muffins.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 15 minutes.