Large Batch Amish Fudge

1 pound margarine
1 pound Velveeta cheese
2 cups nuts, chopped (if desired)
1 cup cocoa powder
2 tablespoons vanilla extract
4 pounds confectioners' sugar

Melt together margarine and cheese. Add nuts, cocoa and vanilla extract; slowly add confectioners' sugar in small amounts; beat well. Pour into buttered pans; chill. Cut into squares.