Place the gooseberries and water a non-corroding saucepan. Cover and cook on a low-medium heat, stirring occasionally, for 20 minutes or until the gooseberries are mushy.

Purée the gooseberries through a strainer to produce about 1 ¼ cups of purée.

Stir the sugar and butter into the warm purée and heat, stirring constantly.

Whisk the eggs and the egg yolk just until mixed, then whisk in a little of the hot gooseberry mixture to heat the eggs.

Return to the pan and cook over low heat, stirring constantly, until the mixture is well thickened, and has reached a temperature of 170°F (75°C).

Pour into a container, cover, and chill.