Place gooseberries in a saucepan and add lemon juice. Cover and slowly bring to the boil over low to medium heat, then reduce the heat and cook till the gooseberries turn to a mush, about 5 minutes.
Let cool slightly then push through a fine mesh strainer to extract as much of the pulp as possible.
Add gooseberry pulp to a double boiler or a metal boil placed over a pot with simmering water (make sure the metal bowl does not touch the water). Add the sugar and butter. Heat whilst stirring till butter and sugar are dissolved.
Slowly pour in the eggs whilst beating. Cook over simmering but not boiling water till the mixture thickens, stirring frequently with a wooden spoon and making sure to also scrape over the bottom and sides of the pan. When the mixture coats the back of the cooking spoon, it is ready.
Pour mixture into sterilised jars and let cool. Close jars with lids. Refrigerate and use within one week, or freeze. If freezing leave a generous amount of headspace (about 3cm) because the curd expands as it freezes.