This is only used for roast lamb in the spring. When the lambs are grown into sheep, the mint is too old for sauce. But they harmonize very pleasantly when both are young.
Take a large bunch of fine fresh green mint, that has been washed well. Strip the leaves from the stems, and mince them small. Put it into a pint bowl, and mix with it gradually some of the best cider vinegar. This sauce must not be in the least liquid, but as thick as horse-radish sauce or thicker. Make it very sweet, with the best brown sugar. Mix it well, and transfer to a small tureen, or a little deep dish with a tea-spoon in it. Serve it up always with roast lamb, putting a tea-spoonful on the rim of your plate.
A quart or more of mint sauce, made as above, but with a larger portion of sugar and vinegar, will keep very well for several weeks, in a jar well corked.
(For modern cooks: Combine 1/2 cup cider vinegar and 1 tablespoon in small saucepan and heat until warm. Add 1/3 cup mint leaves and set aside to cool)
Sources: Eliza Leslie Miss Leslie’s New Cookery Book, Philadelphia, 1857 as found in Nancy Carter Crump, Hearthside Cooking, 1986.