Source: Beth Thompson (one of my former co-workers)
Prepare a brownie mix (the fudgy ones and the chocolate chip ones are best!), following package instructions (I made a 9x9 batch). Allow to cool.
For mint layer:
1 1/2 c. (approximately) powdered sugar
1/3 c. margarine
2 ½ tbsp Crème de Menthe (get the green kind, or buy some food coloring)
Melt butter and mix all 3 ingredients together (I suggest that you add the butter a little at a time because I usually don’t end up using it all). The mint mixture should be thick, but pourable. Spread it over the top of the brownies and put in the fridge to let it stiffen while you prepare chocolate layer on top. You can taste it and make sure it is minty enough before you spread it on there.
1 cup chocolate chips
6 tablespoons of margarine
Melt together in a double boiler. Let it cool for a couple of minutes (keep stirring it). Spread over top of mint layer.
Refrigerate until chocolate topping is stiff (not runny) and cut later.
As you all know I have difficulty following a recipe if I feel that I can improve it. I do not think that the mint layer is enough to fully taste the minty fresh flavor of the Crème de Menthe. So, I usually double the mint layer. Also, when I say, "add the butter a little at a time," I mean it because it usually does not take it all. If you want to make it a thicker mint layer, I would use 3 cups of powdered sugar and start with 2 1/2 Tbsp. of Crème de Menthe and then add more to taste. I am pretty sure that the other day I used about 4 1/2 Tbsp. I think that I do stick with the 1 cup of chocolate chips part, but I may "accidentally" let my cup runneth over.
Another note that I will make is to buy the smallest bottle you can get of the Crème de Menthe because it gets more alcoholic and less minty as time goes by. I would also suggest storing it in your freezer if you have space.
One more note: they will turn out much prettier if you turn them out of the pan and then cut them. I just run a butter knife around the edge and flip them onto aluminum foil and them use another piece of aluminum foil to flip them right side up. Use a sharp knife to cut them.
In case the above picture was not enough to convince you that you want to try these brownies, here is a close-up. Click on the picture to make it full screen.