To prepare the walnut muffins in the air fryer, crack the egg into a bowl, add the sugar, oil, plain yogurt, and a few drops of orange flavor (alternatively, you can add half a level teaspoon of cinnamon). Mix everything with a whisk (or you can use an electric mixer) until you obtain 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 and mix to distribute them in the batter.

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

Decorate the muffins with some chopped or whole walnuts. Place the molds in the basket of the air fryer (in my case, I used a fryer with a capacity of 6 liters) and cook at 329°F for 12 minutes, then lower the temperature to 311°F and cook for another 3-4 minutes.

To make sure they are cooked, do the toothpick test: insert it into the center of the muffin, and it should come out dry. If necessary, extend the cooking for another 2-3 minutes at 311°F.

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