Mint has a sweetness of its own, but a little sugar would be okay if you prefer extra sweetness - no more than 1/2 teaspoon. Cider or malt vinegar can be used for the vinegar. A traditional pairing with lamb.
I like to freeze the mint leaves overnight. It makes it easy to crush up the leaves for the sause - 30 May 2011
Loved this as a great sauce foundation. I added three types of mint: Apple, Spearmint and Black Pepper Mint. I used cider vinegar which is great with the Appley mint and a good sprinkle of caster sugar. Lip-smacking! - 25 Jun 2017
My mom is from England and she has made mint sauce for years. Mint sauce is about the mint not the vinegar... In a sauce pan take a fist full of fresh mint leaves that have been coarsely chopped and place them in the pan with 2 cups of simmering water. Let it simmer on med.low heat for 15 min. then add two level table spoons of white sugar and mix till dissolved; then add three table spoons of apple cider vinegar and simmer for a few more min. Taste to see if you would like more sweet or tart and add some more sugar or vinegar to your liking. The true English Style Mint Sauce has more mint flavor and less tartness. Enjoy. - 07 Jul 2009 (Review from Allrecipes US | Canada)