1 (16 oz.) pkg. light brown sugar
3 tbsp. all-purpose flour
3/4 c. cold water
1/2 c. butter
1 (16 oz.) pkg. confectioners' sugar, sifted
1 tsp. vanilla extract

In medium saucepan, combine brown sugar, flour, water, and butter. Cook over medium heat until sugar dissolves. Continue to cook to 236 degrees on candy thermometer or to just under the soft-ball stage. Cool on wire rack without stirring for about 10 minutes. Add confectioners' sugar and vanilla, beat until icing is of spreading consistency.