Whisk the eggs in a large bowl. Blend in sugar and beat until mixture is thick and pale, about 10 minutes. Mix in the melted butter and salt. Gradually fold in the flour and lemon zest. Cover and refrigerate for at least one hour or preferably overnight.
Preheat oven to 165 degrees C. Lightly grease baking tray.
On a floured surface roll out dough to 5mm thickness. Cut into desired shapes using biscuit cutters. Place biscuits on prepared baking tray. Brush with beaten egg yolks and decorate with sprinkles.
Bake in preheated oven until golden at the edges, 15 to 20 minutes. Cool biscuits on racks.