Mix the flour and the cornflour with the sugar and baking powder. Make a well in the middle and add the eggs, salt, lemon zest and soured cream. Grind the almonds very finely in a food processor and add them to the dough.
Cut the butter into little chunks and add it to the dough. Quickly knead all ingredients into damp but not sticky dough. Add a few teaspoons flour if the dough is too moist, or a few drops of water if it is too dry. Cover and refrigerate for 30 minutes.
Roll the dough about 1cm thick and cut out shapes of your choice with large biscuit cutters.
Heat the oil and fry the pieces until golden brown, turning them once. Remove them with a slotted spoon and place them on a platter covered with kitchen paper. Sprinkle a thick layer of icing sugar over the hot doughnuts, using a sieve. Serve within the next hour or two.
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