Preheat your oven to 190°C (375°F). This will ensure that your muffins bake evenly and rise beautifully.
Line your muffin tin with parchment paper or muffin liners to make removing the muffins easy once they’re baked.
In a small saucepan, melt the 80g of butter over low heat. Once melted, set it aside to cool slightly.
In a large mixing bowl, whisk together the melted butter, almond or peanut butter, and sugar until smooth. Add in the eggs, vanilla extract, and orange zest (if using), and mix until well combined.
In another bowl, sift together the flour, oats, and baking powder. This will help to aerate the flour and ensure the ingredients are evenly distributed.
Gradually add the dry ingredients to the wet mixture, alternating with the milk. Stir until just combined; be careful not to overmix. The batter should be thick but pourable.
Gently fold in the blueberries and the chopped walnuts or almonds, taking care not to break the berries.
Spoon the batter into the prepared muffin tin, filling each cup about ¾ full. This allows room for the muffins to rise.
In a small bowl, mix together the remaining oats and brown or white sugar. Sprinkle this mixture generously over the muffin batter.
Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. The tops should be golden brown.
Once baked, remove the muffins from the oven and let them cool in the tin for 5 minutes. Then transfer them to a cooling rack to cool completely. Enjoy warm or at room temperature!
