1-1/4 cups sugar
1/4 cup cornstarch
1/4 teaspoon salt
3 cups milk
3 ounces unsweetened chocolate, chopped
4 egg yolks, lightly beaten
3 tablespoons butter
1-1/2 teaspoons vanilla
1 9-inch pie shell, baked
In a large saucepan, combine the sugar, cornstarch and salt. Stir in milk and chocolate.
Cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. Remove mixture from heat.
Stir a small amount of the hot filling into the egg yolk. Then, return the egg mixture to the remaining filling, stirring constantly. Bring to a gentle boil being careful not to burn mixture. Cook and stir 2 minutes longer. Remove from heat.
Gently stir in butter and vanilla. Spoon mixture into baked pie shell. Cool on a wire rack. Cover and chill for at least three hours before serving.