Elderflower Lemon Curd

1 good handful elderflower umbels (about 5)
1 cup sugar
1/2 cup freshly squeezed lemon juice
4 large eggs, lightly beaten
1 stick unsalted butter, chilled and cut into small pieces

Gently shake elderflower umbels to remove any insects.
Remove as much of the green stems as possible.
The best way to do this is to strip them off the stems with your fingers into a bowl.
Combine sugar and lemon juice in a small saucepan over low heat.
Cook and stir until sugar is dissolved in the warm liquid.
Add elderflowers, turn off the heat, and let steep for 1 to 2 hours.
Strain mixture through a fine sieve into a double boiler or a metal bowl placed over a saucepan with simmering water.
Squeeze the elderflowers to extract as much of the liquid as possible.
Add eggs to the double boiler and cook over simmering water, stirring often with a wooden spoon,
until mixture coats the back of the spoon, about 10 minutes.
Make sure to scrape over the bottom and the sides of the double boiler.
Once mixture is thick, remove from the heat.
If it seems a bit lumpy, strain it through a fine sieve again.
Add butter and stir until fully dissolved.
Pour into a jar with a tight-fitting lid and refrigerate or freeze.