An easy penuche fudge recipe involves bringing 1 1/2 cups sugar, 1 cup brown sugar, 1/3 cup light cream, 1/3 cup milk and 2 tablespoons butter to a boil. Cook the mixture for 10 to 15 minutes, add 1 teaspoon vanilla after cooling and spread in a pan. The fudge can be cut when firm.
Martha Stewart's more sophisticated recipe for penuche fudge begins by coating a 5-by-10-inch loaf pan with cooking spray and lining it with plastic wrap. In a medium saucepan, bring 5 ounces of evaporated milk, 1 1/2 cups packed light brown sugar, 5 ounces of butter and 1/4 teaspoon salt to a boil while stirring constantly. Reduce the heat to medium-low, letting the mixture simmer until it reaches 236 degrees Fahrenheit on a candy thermometer, which takes about 25 minutes.
Put the mixture into a mixing bowl, and beat in 1/2 cup confectioners' sugar on low speed. Increase the speed to medium until the mixture has thickened and is smooth, which takes two to four minutes. Return the speed to low to add 1 teaspoon pure vanilla extract and 3 ounces chopped, toasted walnuts. Spread the mixture in a pan, and smooth the top. Refrigerate uncovered for about 25 minutes or until firm.