We mix the yeast with the lukewarm milk until it mixes well. We place the flour, salt, margarine and eggs in the mixer bin and we stir on the low scale. We add sugar and essential oil. We slowly add the milk to the yeast. We stir until the dough is peeled off the mixer walls. In a floured bowl we place the dough, we cover it with a cloth and we let it expand for 30 minutes. On a floured surface, we knead the dough a little and we roll out a sheet of about 3-4 mm thick. With the help of a cup, we cut small pies. In the middle of the half we place 1 tablespoon of jam. We spread with the egg whites and we close with the rest of the halves by squeezing the edges well. We put them on non-stick paper, gently pressing them down and we cover them with a cloth for 15 minutes to expand at room temperature. In a saucepan, we heat the oil and, with the help of a ladle with holes, we dive the balls. We fry on both sides. We let the doughnut drain on an absorbent paper. Then we sprinkle with caster sugar.