Preheat your oven to 180°C (350°F). Grease your muffin tin or line with paper liners, and gather your tools.
Peel and dice the apples into small, even pieces. Toss them with a teaspoon of lemon juice if you like, to prevent browning and add a hint of brightness.
In a large mixing bowl, combine the oats, whole wheat flour, brown sugar, baking powder, and cinnamon. Mix until well blended and the mixture looks evenly distributed.
In a separate bowl, whisk together the eggs, melted butter, vanilla extract, and milk until the mixture is smooth and slightly frothy.
Pour the wet mixture into the bowl with the dry ingredients. Gently fold everything together with a spatula until just combined—don’t overmix, some lumps are okay.
Gently fold in the diced apples, distributing them evenly throughout the batter. Be careful not to break down the apples too much.
Scoop the batter into the prepared muffin tin, filling each cup about three-quarters full. Tap the tin lightly on the counter to settle the batter and release any air bubbles.
Bake in the preheated oven for 20-25 minutes, until the muffins turn a golden brown and a toothpick inserted into the center comes out clean.
Remove the muffins from the oven and let them cool in the tin for 5 minutes. Then transfer them to a wire rack and allow to cool completely or serve slightly warm.
Enjoy these moist, flavorful muffins plain or with a pat of butter, perfect for a cozy breakfast or snack.
