Chocolate Marshmallow Fudge

1/4 cup butter
2 cups sugar
2/3 cup evaporated milk
2 cups (12 ounces) semisweet chocolate chips
1 jar (7 1/2 ounces) marshmallow creme
1 cup chopped pecans
1 teaspoon vanilla
pecan halves for garnish, optional

Heat butter in a heavy 3-quart skillet over low heat. Add sugar and evaporated milk; stir over medium heat until mixture comes to a rolling boil.

Continue to boil for about 4 minutes, or until a candy thermometer registers 226°. Remove from heat. Add chocolate chips; stir until melted.

Stir in marshmallow creme, pecans, and vanilla until well blended. Pour into a greased 9-inch square baking pan. Place on rack to cool.

Refrigerate for several hours, or until cool enough to cut into squares. Cover and store in refrigerator.