Line an 8x8x2-inch baking pan with foil, extending foil over edges of pan. Butter the foil; set pan aside.

Butter the sides of a heavy 2-quart saucepan. In the saucepan combine granulated sugar, milk, chocolate, and corn syrup. Cook over medium-high heat to boiling, stirring constantly with a wooden spoon to dissolve sugar. This should take about 5 minutes. Avoid splashing mixture on sides of pan. Carefully clip candy thermometer to side of pan.

Cook over medium-low heat, stirring frequently, until thermometer registers 234 degree F, soft-ball state. Mixture should boil at a moderate, steady rate over the entire surface. Reaching soft-ball stage should take 20 to 25 minutes.

Remove pan from heat. Add the 2 tablespoons butter and vanilla, but do not stir. Cool, without stirring, to lukewarm (110 degree F). This should take about 55 minutes.

While the fudge is cooking, prepare the mint mixture. Place the 3 tablespoons butter and the creme de menthe into a small mixer bowl. Beat with an electric mixer on high speed until fluffy. Add the powdered sugar and beat until smooth. Cover and set aside.

Remove candy thermometer from saucepan. Beat vigorously with the wooden spoon until fudge becomes very thick and just starts to lose its gloss. This should take about 7 minutes. Quickly turn fudge into prepared pan. Dollop mint mixture over fudge; press mint mixture evenly over fudge. Sprinkle nuts over mint mixture; press in lightly. While fudge is warm, score it into 1-inch squares. When candy is firm, use the foil to lift it out of the pan; cut candy into squares. Store tightly covered. Makes 64 pieces or about 1-3/4 pounds.

Up to 2 weeks ahead prepare fudge. Store in the refrigerator in a tightly covered container.