In a separate bowl, mix or whisk together your dry ingredients (flour, baking powder, sugar, salt & cinnamon), set aside.
In another large bowl, using a rubber spatula or wooden spoon, mix together the wet ingredients (milk, butter, Greek yogurt/sour cream, eggs & vanilla) for the muffins. Make sure to use very softened butter or partially melted butter but make sure the butter isn't hot!)
Slowly begin mixing in your dry ingredients for the muffins into the wet ingredients a little at a time, blending as you continue adding in the dry ingredients.
Fold or mix in the chopped apples.
Using a large cookie or ice cream scoop, fill your muffin tins/liners all the way to the top.
Get the crumble mixture out of the fridge and crumble it up as you like and sprinkle it on top of the muffins.
Bake for 18-20 minutes.