A true classic, this fudge frosting recipe takes any cake from tasty to mouthwatering. Making this frosting can be tricky, so be sure to follow our instructions so it turns out just right.
When the mixture is super hot, any contact with uncooked sugar molecules that may be on the side of the pan can cause the mixture to crystallize and seize. The mixture will become grainy and hard. If this happens, you'll have to start over, so be sure to stir carefully while heating the mixture so no sugar is left behind.
Heating fudge frosting to the right temperature is key, so before getting started, check the accuracy of your candy thermometer. To do this, bring a saucepan of water to boiling. Check the temperature your thermometer registers in the boiling water. Add or subtract the number of degrees it is off from 212 degrees F when measuring the temperature of frosting.
After calibrating your candy thermometer, clip it to the side of a 3-qt. saucepan. Combine 2 oz. unsweetened chocolate, chopped; 3 cups sugar; 1 cup milk; 3 Tbsp. light-color corn syrup; and 1/4 tsp. salt in the saucepan. Heat and stir over medium heat to dissolve sugar. Bring to boiling over medium-high heat, stirring constantly.
Reduce heat to medium, maintaining a moderate, steady boil until mixture reaches 232 degrees F, 6 to 8 minutes, stirring occasionally (keep a close eye on the temperature). Immediately remove the saucepan from heat and place on a wire rack, being careful not to slosh the mixture. Add 1/4 cup butter on top of the mixture, but do not stir or disturb the mixture.
Allow the butter to melt on top of the mixture. Do not stir the mixture while butter is melting. Let the mixture cool to 110 degrees F; this should take about an hour.
Once the mixture has cooled and the butter is completely melted, add 1 tsp. vanilla. Beat with a mixer on low until frosting thickens and lightens in color, about 20 minutes. The mixture will still appear loose and should have the consistency of a thick glaze. Set the mixture aside; it will continue to thicken as it stands at room temperature, so keep checking it every few minutes to see if the consistency is right for spreading.
Once the frosting has reached spreading consistency, spread it on your favorite cake or cupcake recipe (or sneak a spoonful for yourself). For a truly showstopping dessert, we recommend spreading it on this classic Devil's Food Cake recipe.
Any cake or cupcake recipe will be heavenly with a dollop of fudge frosting on top. But if you don't already have a recipe in mind, we have a few suggestions that could use a good coat of frosting.
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