For the lemon butter, beat the whipping cream in a mixing bowl with a mixer until the fat separates from the liquid. Strain the buttermilk.
Wash the butter with cold water, squeeze well and place in a small bowl. Mix the zest of half an organic lemon, a squeeze of lemon juice and sea salt to taste, with the butter (this is best done with a fork).
Pour into a small container with a lid and leave to infuse briefly in the refrigerator.