The day before for the caramel cream, place unopened condensed milk cans in a pot, cover with water and heat covered. Simmer for about 6 hours. (Attention! Cans must always be covered with water.) Take out cans and put them in a cool place overnight.
The next day, for the shortbread base, mix butter, sugar and icing sugar with the whisks of the mixer for about 5 minutes until light creamy. Mix 1 pinch of salt, flour and starch and stir into the butter mixture.
Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line a box form (11 x 30 cm; approx. 1.8 l capacity) with baking paper (see page 15). Press the dough into the tin with a spoon.
Bake in a hot oven for 40-50 minutes.
Chop 100 g chocolate coating. Remove cake from the oven. Immediately sprinkle the chopped chocolate coating over it and let it melt. Let it cool down in the mould.
Open condensed milk tins and spread the boiled down caramel cream on the cake. Chill for about 30 minutes.
Chop 250 g chocolate coating. Melt in a hot water bath, let it cool down for about 15 minutes. Lift the cake out of the mould using the paper. Spread the couverture on the cake, pressing grooves into the surface with a teaspoon.
Chill for about 15 minutes.