Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease a box form and dust with flour. For the dough, mix 150 g butter, 75 g icing sugar and 1 pinch of salt with the whisks of the mixer until creamy.
Stir in the eggs one by one. Stir in 200 g condensed milk. Mix 150 g flour and baking powder, stir in briefly.
Approx. 1⁄3 Smooth the dough in the mould and place the pastry sandwiches on top. Heat the milk. Dissolve espresso and cocoa powder in it, stir in cinnamon. Stir into the remaining dough. Spread the dark dough on the biscuits.
Bake in a hot oven for 40-45 minutes (chopstick test). Leave the cake to cool in the tin for approx. 45 minutes. Then loosen the edges with a knife. Turn over carefully. Let it cool down.
For the milk freezing rest, whip condensed milk with lemon juice and cream until stiff for approx. 3 minutes. Whip 75 g soft butter and 25 g icing sugar until creamy. Stir the condensed milk cream into the buttercream by the spoonful and spread on the cake.
Chill for at least 1 hour.