Preheat oven to 375°F. Line a 12-cup muffin tin with muffin liners or lightly grease the muffin tin with butter.
Pour your jar of the Healthy Make Ahead Muffin Mix into a large bowl. If your mix-ins contain dry ingredients, such as chopped nuts, raisins, or chocolate chips, add them to the dry ingredients and mix well to combine. You want to make sure that the mix-ins are well coated with the flour. Set aside.
In a second bowl, combine the melted butter (or oil if using), milk, yogurt, eggs, and extract. Mix well to blend thoroughly. If your mix-ins include wet ingredients, such as mashed banana, apple sauce, or pumpkin puree, add them to the wet ingredients and mix well to combine.
Add the wet ingredients to the dry ingredients. Fold the mixture gently until the dry ingredients are just moistened. DO NOT OVER MIX! The batter will be lumpy. Fill muffin cups to almost full, leaving a small amount of room for the crumb topping.
Add a tablespoon or more of crumb topping to the top of each muffin. (See Crumb Topping instructions below.)
Place your filled muffin tin on the middle rack of the preheated oven and bake for 25-35 minutes until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffin tin from the oven and allow the tin to cool on a wire rack.
Once cool, remove the muffins from the muffin tin. Serve or store the muffins well wrapped in the refrigerator. Muffins will stay fresh refrigerated for 2-3 days.