Combine butter & salt.
Mix egg yolks & sugar w/ your haldheld electric mixer until fluffy.
Add butter-salt mess & mix thoroghly.
Add flour & baking powder & mix. Afterwards knead the dough w/ your hands.
Divide the dough into 2 & place each part on cling foil. Roll in cling foil until round.
Place in the fridge (fresh department at almost 0° C!) for about 30 min.
Preheat the oven to 160° C w/ fan.
Line 2 baking sheets w/ baking parchment.
Cut the dough rolls into slices of about 5 - 6 mm & arrange on the baking sheets.
Mix egg & water & brush the cookies w/ the egg wash.
Bake for about 15 min. Afterwards let them cool properly before storing in a container.