Softened butter stir the mixer on low speed for 2-3 minutes, until fluffy. Gradually add sugar, stir another 1-2 minutes, add the essence and grated lemon rind. The yolks of the eggs were removed and added to the bowl one by one. Stirred with mixer for a few minutes. Parts dough to add sifted flour and milk alternately until mixed well. Separated in a dry bowl egg whites are broken down into snow and gradually, three times is added to the dough. Stir with a spatula (not with a mixer). Half of the dough is transferred into another container and to it gradually add the cocoa until fully assume. In pre-greased and floured cake pan is placed part of the cocoa dough until it is put on the white batter, then again from cocoa, again by alternating white and checkered, while allocated in the form. Bake 40-50 minutes in preheated to 170 ° C oven. The glaze is prepared by the chocolate is melted over low heat 4-5 tbsp of milk and spread on cake up the cold.