Preheat oven to 400˚F and follow the instructions on the box to make the muffins in a large mixing bowl.
To make the crumble topping, combine the sugars, nutmeg, and salt in a small/medium bowl. Pour in melted butter and slowly whisk in the flour. Stir together using a rubber spoon/spatula until the mixture in combined and crumbly.
Prepare a muffin tin with silicone, or, paper liners. Pour enough blueberry muffin batter to fill each tin 3/4 of the way full. Top each muffin with a generous helping of the crumble topping and gently push the topping into the muffin mix to keep it in its place while baking.
Bake the muffins in the oven for 20-22 minutes until they're golden brown on top and pass the toothpick test.
Remove from the oven and let the muffins rest in the tin for 5-10 minutes. You can then either move the muffins to a cooling rack to cool completely, or my personal favorite, smear with butter and enjoy!
