I only make these over the holidays. 1. Because I can eat all of them myself and 2. Because they are a little time consuming. I will try to make them early for Thanksgiving and try freezing them this year. I think I could probably eat these frozen. I am not a real mint fan but these are yummy. 
1 cup butter-softened & divided
1 cup sugar
4 eggs
1 cup flour
1/2 tsp salt
1 16 oz can chocolate syrup (I use Hersheys)
1 tsp vanilla
2 cups powdered sugar
2 Tbsp Creme DeMenthe (or less)
6 oz semi-sweet chocolate chips
Cream 1/2 cup butter. Gradually add 1 cup sugar, beating till light and fluffy. Add eggs 1 at a time beating well after each addition. Combine flour, salt and add to creamed mixture, alternating with chocolate syrup, beginning with syrup and ending with flour. Stir in vanilla. Pour into buttered and floured 13x 9x 2" pan. Bake 350 degrees for 25-28 minutes. Cool completely.
Cream 1/4 cup butter. Gradually add 2 cups powdered sugar and Creme DeMenthe. Mix well and spread over brownies. Chill for 1 hour.
Combine chocolate chips and 1/4 cup butter in top of double boiler until melted (or microwave slowly). Spread quickly over brownies. Chill for at least 1 hour. Cut into 1" squares. Brownies will shrink from sides of pan.
You can usually speed up these cooling processes by sticking your pan in the freezer. At first I had trouble finding CremeDeMenthe. I have used CremeDeMenthe Liquor but it isn’t as strong as the flavorings and if you use too much it can make your middle layer a little too soft. You can find this where they have cake supplies or I get mine online.
The one from the Great American Spice Company is very strong so go easy if you use that one. Start out a tsp at a time and taste.