Preheat your oven to 400°F (200°C) and line a 12-cup muffin tin with paper liners (or coat with butter or nonstick spray).
In a large bowl, cream together the softened butter and brown sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract and milk.
1/2 cup butter, 3/4 cup brown sugar, 1 tsp vanilla extract, 2 eggs, 3/4 cup whole milk
In a separate bowl, whisk together the wholemeal flour, oats, cinnamon, baking powder, and salt.
Gradually add the dry ingredients, grated carrots and apple, and raisins to the wet ingredients, mixing until just combined. Be careful not to overmix!
1/2 cup raisins, 1 cup grated apple, 1 cup grated carrots
Divide the muffin batter evenly among the prepared muffin cups using an ice cream scoop for mess-free filling.
Bake for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Let the carrot apple muffins cool in the pan for a few minutes before transferring them from the muffin tray to a wire rack to cool completely.
Notes
Don't overmix: Overmixing can lead to tough muffins. Once the dry ingredients are just incorporated, stop mixing.Grate apple and carrots: Grating the apple and carrot ensures they are evenly distributed throughout the batter and bake evenly.Double batch: Make a double or triple batch and freeze half once cooled for on-demand lunchbox fillers and snacks.