Defrost the blueberries. Put the fat and sugar in a bowl and whisk with the whisk of the hand mixer until foamy. Gradually stir in the eggs. Wash the lemon, dab dry, finely grate the peel and add.
Mix flour and baking powder and stir it with the milk, spoon by spoon, into the fat-egg yolk-sugar mass. Halve the lemon, squeeze out the juice and carefully fold into the dough with the blueberries. Grease a box form (26 cm long) and sprinkle with breadcrumbs.
Pour in the dough, smooth it down and bake in a preheated oven (electric: 175 °C/ gas: level 2) for 60-70 minutes. If necessary, cover with parchment paper 10 minutes before the end of the baking time. Turn the cake out of the tin onto a cake rack.
Dust with icing sugar. Whipped cream tastes good with it.