Sift flour and mix it with white sugar and salt. Grate cold butter into the flour blend. Stir accurately to make flour combine with butter. Set aside 1 cup of this blend.

Follow next steps using the second part of the flour blend: put soda and baking powder in it, pour kefir, add vanilla extract and knock in a raw egg. Keep beating the dough with a mixer until it becomes a fluffy mass of light colour.

Mix deferred flour crumbs with brown sugar. Put ½ of dough on a baking dish, covered with parchment (Ø20 cm), then spread a layer of confiture and lay out another layer of a dough afterwards. Sprinkle crumbs on the top. Bake the cake at a temperature of 180 C for 50-55 minutes.