Melt the butter in a saucepan.
Add lemon juice and zest, elderberry syrup and the sugar to the butter and mix well.
Crack the eggs, whisk well in a bowl and pass through a sieve. Add to the butter mixture, stirring constantly. Stir over medium heat until a pudding-like consistency is reached.
Pour into jars and store in the refrigerator. The mixture will firm up a bit more in the refrigerator.
Preparation Tip:
Shelf life: about 2 weeks in the refrigerator.