Beat butter or margarine in a large bowl until softened. Add sugar and beat until fluffy. Add egg, verjuice, and almonds, and beat well.
Combine flour and baking soda and slowly add them to the butter mixture. Beat until well mixed.
Cover the bowl and put it into the fridge for at least an hour.
Grease a baking sheet or use baking parchment.
On a slightly floured surface, form a heaped tablespoon of dough into a stick as thick as a finger and put it on the sheet. Make sure to keep enough distance between the pieces!
Mix the egg yolk with verjuice and brush onto the formed cookies, then decorate with the sliced almonds.
Bake until golden for about 15 minutes in the preheated oven at 160 ºC (convection oven) or at 175 ºC (top/bottom heat).