Preheat oven to 350 degrees.
Grease 15 1/2" x 10 1/2" jelly-roll pan.
In heavy saucepan over low heat, melt chocolate squares until smooth, stirring constantly.
In large bowl at low speed, beat sugar, corn syrup, vanilla and butter or margarine just until blended.
Increase speed to high beating until light and fluffy.
Reduce speed to low and add flour, salt, and eggs. Beat until well mixed, constantly scraping bowl with rubber spatula.
Increase speed to high and beat 2 minutes.
At low speed, mix in melted chocolate until blended.
Stir in walnuts with a spoon.
Evenly spread batter in pan.
Bake 40 to 45 minutes until toothpick inserted in center comes out clean.
Cool brownies in pan on wire rack.

In large bowl at low speed beat powdered sugar, milk, peppermint extract, and butter until smooth.
Stir in enough green food coloring to tint a pale green.
Evenly spread frosting over cooled brownies.
Refrigerate while preparing Chocolate Glaze.

Melt all ingredients in heavy saucepan over low heat until chocolate melts and mixture is smooth, stirring constantly.
Remove from heat and continue stirring until glaze cools slightly.
Pour over Mint frosting layer to completely cover the top.