1Preheat the air fryer to 165°C for 3-5 minutes.
2In a large bowl, mix flour, sugar, baking powder, and salt.
3In another bowl, beat the egg, then add milk, melted butter, and vanilla.
4Pour the wet ingredients over the dry and mix gently until just combined (do not overmix).
5If using, gently fold in blueberries, chocolate, or nuts.
6Fill silicone muffin cups about 2/3 full and place them in the air fryer basket.
7Bake at 165°C for 12-15 minutes, until a toothpick inserted in the center comes out clean.
8Carefully remove muffins, let cool for 5-10 minutes, and serve warm or at room temperature.