To prepare the walnut and chocolate muffins in an air fryer, break the egg into a bowl, add the sugar, oil, plain yogurt, and a few drops of orange flavor (alternatively, you can add half a teaspoon of cinnamon). Mix everything with a whisk (alternatively, you can use a hand mixer) until you get a smooth and homogeneous mixture.

Add the previously sifted baking powder and flour and continue to mix to combine everything. Add the coarsely chopped walnuts, chocolate chips, and mix to distribute them in the batter.

Take the aluminum molds, butter and flour them, then fill them with 3/4 of the batter. Alternatively, you can line the aluminum molds with paper muffin liners.

Decorate the muffins with some chopped walnuts and chocolate chips. Insert the molds into the air fryer basket (in my case, a 6-liter capacity fryer was used) and cook at 330°F for 12 minutes, then lower the temperature to 311°F and cook for another 3-4 minutes.

To ensure they are cooked, do the toothpick test: insert it in the center of the muffin and when you pull it out, it should be dry. If necessary, extend the cooking time by another 2-3 minutes at 311°F.

Once cooked, let the walnut muffins cool on a wire rack. Once they have cooled, you can enjoy them. If you wish, you can sprinkle them with powdered sugar.