(This is so simple, it really shouldn't count as a "recipe.")
Boil 2 cups of water. Remove from heat and add mint leaves to steep. Cool in the refrigerator.
Once it's cool, strain (or pick) the mint leaves out of the water. Use the mint water as part of the liquid for making lemonade. For example, I like the Minute Maid Lemonade that's made from concentrate. Use the mint water, then any additional water that the concentrate directions call for.
Use additional mint leaves for garnish, if desired.