Preheat oven to 180°C normal heat (static)
Whisk the eggs and sugar for 5 min until pale. using a stand mixer or hand mixer.
Add the oil while mixing, then add the milk and lemon juice.
Stir in lemon zest, chopped walnuts and flour sifted with baking powder. Mix well.
Using an ice cream scoop, fill the muffin cups three quarters full.
Place a walnut kernel on each muffin.
Bake for 25 minutes more or less. Check the doneness of the muffins by inserting a skewer into the center. It should come out dry.
Place the muffins on a wire rack and leave to cool.
Sprinkle with powdered sugar and enjoy with a cup of coffee.