To make copycat McDonald's french fries, soak julienned russet potatoes in a mixture of 1/4 cup corn syrup and 1 1/2 cups water for 30 minutes in the refrigerator, heat peanut oil to 375 degrees Fahrenheit, drain the potatoes and pat dry, partially fry the potatoes for about 1 1/2 minutes, chill the fries for 10 minutes, and finish them up by frying for another five to seven minutes. The multi-step process creates the right crispy exterior and fluffy interior.
For best results, use french fries that are cut to 1/4 inch by 1/4 inch by 4 to 6 inches long. Use a heavy-bottomed pot with enough room for the fries to move around while frying or a deep fryer. Two large russet potatoes make enough french fries to require about 6 cups of peanut oil if they are all cooked at once. During the first fry, remove the potatoes just when they start to turn brown, usually between one minute and 1 1/2 minutes.
After the first fry, drain the french fries on paper towels to remove extra oil, and then immediately place the french fries in the refrigerator. For extra flavor, add 1/4 cup of beef fat to the peanut oil while the fries are chilling, and increase the oil to 400 degrees Fahrenheit at this point for extra crispy fries.