Core the apple with an apple corer and cut it into thin slices, around 4-5mm thick. Sprinkle them with a couple of drops of lemon juice and set aside.
Separate the egg yolks and egg whites of two eggs
In a bowl whisk together the egg yolks and sugar, until creamy and fluffy.
Add the flour, milk and zest of the lemon, mix well and set aside.
In another bowl whisk the egg whites until they form stiff peaks. Carefully fold the beaten egg whites into the dough mixture.
Heat a little knob of butter in a non-stick pan over medium heat.
Dip the apple slices into the dough until they are well coated, take them out with a spoon and cook them over medium heat on both sides until they are golden brown.
While they are cooking, mix the sugar with the cinnamon in a flat bowl and dip the cooked apple beignets into the mixture until they are evenly coated.
Serve warm together with the vanilla sauce.