How to Make It
In a small saucepan, cook the butter with the salt over moderately low heat until nutty brown, about 5 minutes. Scrape the butter into a bowl and chill in a bowl of ice water, stirring frequently, just until it begins to harden around the edges, about 5 minutes. Remove the bowl from the ice water and gently beat with a wooden spoon until the butter is slightly pale and creamy. Fold in the chopped lemon, sage and lemon zest.
The butter can be wrapped in plastic and refrigerated for up to 5 days.
To make the chopped lemon, cut the skin and bitter white pith from a lemon. Cut between the membranes to release the sections, then chop.