To make brown sugar fudge, boil 3 cups of brown sugar, 3/4 cup of evaporated milk and 1 cup of butter in a large saucepan for 10 minutes. Remove the fudge from the heat, and add 2 cups of confectioners' sugar. Add 1 cup of chopped nuts if desired. Beat the fudge with an electric mixer on medium speed for 5 minutes. Spread the fudge into a greased 8-inch square pan and let it cool.
Alternatively, Completely Delicious provides a slightly more sophisticated approach to making brown sugar fudge. Combine 1/2 cup plus 2 tablespoons of evaporated milk, 2 cups of brown sugar, 3/4 cup of cubed unsalted butter and 1/4 teaspoon of salt into a heavy-bottomed medium saucepan. Bring the fudge to a boil over medium heat, and stir until smooth. Continue to simmer, stirring frequently until a candy thermometer reaches 238 degrees Fahrenheit.
Remove the saucepan from the heat, and pour the fudge into a heat-proof bowl. Add 1/2 teaspoon of vanilla extract, and stir it with a hand-held mixer. Add 1 and 3/4 cups of sifted, powdered sugar in small additions while continuing to beat the fudge with the mixer until smooth. If desired, add 3/4 cup of chopped, toasted walnuts. Spread the fudge into an ungreased 8-inch square pan, and chill it in the fridge for 30 minutes or until firm. Slice the fudge with a sharp knife, and store it in an airtight container for several days.