Source: Better Homes and Gardens
1 (4 ounce) white baking bar
1/3 cup butter or margarine
1 cup granulated sugar
1/2 teaspoon baking soda
1/4 teaspoon salt
1/4 cup buttermilk or sour milk
1 teaspoon vanilla extract
2 cups all-purpose flour
1 tablespoon granulated sugar
1 teaspoon red decorating sugar
Melt the baking bar in a small heavy saucepan over low heat, stirring constantly. Set aside.
Beat the butter in a mixing bowl with an electric mixer on medium to high speed for 30 seconds. Add the 1 cup sugar, baking soda and salt. Beat until combined. Beat in the egg, buttermilk, vanilla extract and melted baking bar until combined. Beat in as much flour as you can with the mixer. Stir in any remaining flour with a wooden spoon. Cover and chill for 1 hour.
Preheat oven to 375 degrees F.
Combine the 1 tablespoon sugar with the red sugar. Shape the dough into 1-inch balls. Roll in the sugar mixture. Place the balls 2 inches apart on ungreased cookie sheets. Bake for about 10 minutes, or until the bottoms are light brown. Cool on racks.