Prickly Pear Beurre Blanc

Gently press peeled prickly pears through a china cap (or large-holed strainer) to remove seeds and catch the juice in a bowl. Put the juice and all the other ingredients (except the butter) in a saucepan, and bring to a simmer. Continue to simmer until the amount of juice has been reduced by three-quarters. Remove from the heat and slowly whisk in the butter one piece at a time, moving the pan on and off the heat so the mixture does not get too hot or too cold. When all the butter is incorporated, strain through a fine mesh sieve and keep warm until ready to serve.