Rinse the gooseberries and put them in a non-corroding saucepan with the water. Cover and cook over low to medium heat, stirring occasionally, for about 20 minutes, or until the gooseberries are very mushy. Puree them through a food mill or a strainer. You should have about 1 1/4 cups of puree. Stir the sugar and butter into the warm puree 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. Pour into a container, cover, and chill. Use this to fill small tartlets, garnishing them with rosettes of creme de Chantilly; or fill a 9-inch pre-baked tart shell with the curd and pipe rosettes of creme Chantilly over the top, leaving a small spot uncovered in the center so the curd will show. This also makes a delicious filling for cakes. Like most high-acid fruit curds, this will keep at least two weeks in the refrigerator. Creme Chantilly: Whip the amount of cold fresh cream needed for your recipe until it mounds softly and will just barely hold its shape. The volume will approximately double after it is whipped. There should be no hint of graininess, which is the first sign that the cream is overbeaten and turning to butter. Stir in vanilla and sugar to taste. Or you may flavor the cream with spirits or liqueurs, wine, fruit purees or jams, or the reduced liquid from poached fruit.