First had these from a neighbor years ago, but I lost the recipe. I think this replicates it nicely. Creme De Menthe is a creamy, minty liqueur that's often used to make beverages and desserts. You can find it at most liquor stores. You can purchase clear or green Creme De Menthe, of course to get this fabulous green color in the minty layer I would highly suggest you get the green version. You use very little of the liqueur in this recipe, but the bottle will last a lifetime, it is fairly inexpensive. Maybe $6 a bottle. The brownie part is very rich and dense.