Wash the lemons hot, grate them dry and grate the peel. Halve the lemons and squeeze. Measure out 100 ml juice.
Mix 250 g butter, 250 g sugar, lemon zest and 1 pinch of salt with the whisks of the mixer for about 5 minutes until creamy. Stir in the eggs one after the other. Mix 200 g flour, starch and baking powder.
Alternately fold in the flour mixture with lemon juice. Pour the dough into a greased, flour-blasted box form (30 cm long; min. 2 l capacity) and smooth it down. Bake in a hot oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer) for about 50 minutes.
Take out the cake and let it cool down for about 20 minutes. Then turn out, spread with 2 tbsp. jam and let it cool down completely.
Shortly before serving, whisk the crème fraîche, whipped cream and 2 tablespoons of sugar until stiff with the whisks of the mixer. Carefully stir the rest of the jam with a tablespoon into the crème fraîche cream. Spread the lemon cream on the cake with a spoon.