Gluten Free Apple Crumb Muffins

Name: Gluten Free Apple Crumb Muffins
Prep time: 15 min
Cook time: 30 min
Total time: 45 min
Cuisine: American
Ingredients: 3 cups (420 g) Kim's gluten free flour blend ((or any blend containing xanthan gum)); 4 tsp baking powder; ½ tsp salt; 2 tsp cinnamon; ½ cup (100 g) granulated sugar; 1½ cups (360 ml) buttermilk (milk or dairy-free milk may be substituted); ½ cup (120 ml) canola or vegetable oil (melted coconut oil may be substituted); 2 large eggs, at room temperature; 1 tsp vanilla extract; 2 cups apples, peeled and diced to ¼-inch size (any apples will work, but I like Rome or golden delicious); ½ cup (100 g) lightly packed light brown sugar; ¾ cup (105 g) Kim's gluten free flour blend ((or any blend containing xanthan gum)); ½ tsp ground cinnamon; 6 tbsp (85 g) butter, softened