The actual recipe for Frangos appears to be a carefully guarded document. I found this version online at iChef.com:
12 ounces chocolate
A few drops of peppermint extract
1/2 cup margarine
1 1/2 cups powdered sugar
Two teaspoons vanilla
Melt chocolate in a double boiler and set aside to cool. Cream together margarine, sugar, eggs and vanilla.
Add cooled chocolate and a few drops of mint to creamed mixture.
Pack into 8-inch-square pan. Refrigerate to set. Cut into squares.