For the Sacher spread, hard boil the eggs, rinse in cold water and cut in half. Mash yolks with a fork and mix well with spreadable butter and curd.
Finely chop the egg whites and mix in. Peel onion and chop finely. Remove anchovy rings from the can, drain well and chop finely.
Mix onion, anchovy rings, paprika powder and mustard into the yolk mixture and season the Sacher spread with salt and pepper.