Hard boil eggs for 10 minutes. While still warm peel eggs and remove egg yolks. Push yolks through a fine sieve. Reserve whites for another use. In a bowl stir the egg yolks with 2 tablespoons of the butter till smooth. In a separate bowl beat the rest of the butter with an electric mixer till creamy. Add sugar and lemon zest and beat till combined.
Stir in egg yolk mixture and soured cream. Sift 1/3 of the flour onto the mixture and fold in with a spatula, do not stir at this point. Sift the rest of the flour on top and fold it in as well.Divide the mixture into 4 equal parts, wrap in cling wrap and refrigerate for 2 hours.
Preheat your oven to 200 C / Gas 6. Line a baking tray with greaseproof paper. Generously dust your work surface with flour. Divide every piece into 4 equal pieces and roll to a pencil thin rope of 40cm length. Cut ropes in half and shape each into a pretzel. Place pretzels on the baking tray.
Stir egg yolks with milk and brush on the pretzels. Sprinkle with pear sugar. Bake in the preheated oven till light golden, about 15 to 20 minutes.