How to cook
Stir together the dry and wet ingredients to obtain a homogeneous mixture. Finally, mix it with the grated apples. Distribute the mixture into the already prepared and oiled muffin cups.
In each, distribute some topping. For the topping, cut the firm butter into pieces and mix it with the flour, brown sugar and cinnamon until you get crumbs.
Put the muffins with oats and apples to bake in a preheated 356°F (180 °C) oven for about 20 minutes.