Step 1

Line a 9-inch square pan with aluminum foil, making sure there is a 1-inch foil overhang on the sides of the pan. Grease the foil with 1-1/2 teaspoons butter. Set the pan aside. Editor’s Tip: Forgetting to butter the pan is one of the most detrimental candy-making mistakes. An unbuttered pan will lead to the fudge solidifying in it (not good!).

Step 2

In a large, heavy saucepan, combine the sugar, sour cream and remaining 1/4 cup butter. Cook and stir the mixture over medium heat until the sugar is dissolved. Bring the mixture to a rapid boil, and cook and stir until a candy thermometer reads 234°F (soft-ball stage), about five minutes. Editor’s Tip: Curious about soft-ball stage’s appearance? Our guide on how to make candy has pictures of what the different sugar stages look like.

Step 3

Remove the saucepan from heat. Stir in the white chocolate and marshmallow cream until they're melted. Fold in the peppermint candy and extract. Pour the fudge into the prepared pan.

Step 4

Chill the fudge until firm. Using the foil overhang, lift the fudge out of the pan. Gently peel off the foil, and cut the fudge into 1-inch squares. Store the fudge in an airtight container in the refrigerator.