Prepare the pastry yeast dough. To do this, mix kefir and water, heat the mixture to a pleasantly warm temperature.
Add yeast and sugar. All mix, cover and leave in a warm place for 15-20 minutes or until the foam caps.
Separately, mix 500 grams of flour, vanilla and salt.
In a small bowl with a fork lightly beat into a soft mousse egg at room temperature.