Beat the egg and 100 g of sugar with a mixer. Add the melted butter, yogurt (kefir), and mix.
Add the sifted flour, cocoa, baking soda and baking powder.
Mix everything until a homogeneous mass.
Fill the pastry bag with the resulting mass . Squeeze out in the form of round cakes on a baking sheet covered with parchment , at a distance of about 4 cm. Bake for 9-10 minutes at a temperature of 180°C. Put on a grid, cool.
Filling: fill the gelatin with 30 ml of water, leave for 30 minutes to swell. Heat until gelatin dissolves . In a saucepan, pour 110 g of sugar, pour 30 ml of water, heat until the sugar dissolves . Pour a thin stream of sugar syrup into the gelatin, beating with a mixer until the mass thickens.