Preheat oven to 375. Cream butter and sugar, Beat in eggs one at a time. Melt chocolate in a double boiler. Stir into butter and egg mixture. Sift flour with salt. Add flour alternately with milk. When the batter is smooth, stir in vanilla, mint and nuts. Bake in 20 cm square cake pan for 50 minutes.
Serve chilled, plain or iced with a simple chocolate glace decorated with sugared mint leaves. Sugar leaves by taking leaves flushed with cold water, dipping them in eggs whites and rolling them in fine granulated sugar. Dry on waxed paper.