First mix the butter, sugar, salt, egg and lemon zest with the dough hook of a hand mixer.
Warm the milk slightly and dissolve the yeast in it (the milk must not get too hot). Then mix with the flour alternately with the other ingredients. Finally, add chocolate chips or raisins if necessary. Then place small balls (approx. 50 g each) of the dough on a prepared baking sheet and let rise for approx. 45 minutes. Finally brush with egg yolk
Bake in a hot oven at 175 ° C for about 15 minutes.