Fennel Sauce

English fennel sauce, for salmon and other fish, is based on English butter sauce, and since this version omits the usual flour, it’s really a beurre blanc made with plain water. Use freshly cut fennel.

1 cup (a 250-ml measure) lightly compacted chopped fennel foliage (no stems)

½ pound (250 gr) unsalted butter, in small cubes

salt and white pepper

½ lemon,…