• Bring Water and Milk to boil over high heat.
• Stir in Macaroni and reduce heat to medium-low.
• Cook, stirring frequently until Macaroni is soft (slightly past al dente), 6 to 8 minutes.
• Add American Cheese, Mustard, and Cayenne Pepper.
• Cook, stirring constantly until cheese is completely melted, about 1 minute.
• Turn off heat, stir in Cheddar until evenly distributed but not melted.
• Cover saucepan and let stand for 5 minutes.

Topping

• Stir Panko, Oil, Salt, and Pepper in frying pan until Panko is evenly moistened.
• Cook over medium heat, stirring frequently until Panko is evenly browned, 3 to 4 minutes.
• Take off heat, sprinkle Parmesan over Panko mixture and stir to combine. Transfer Panko mixture to a small bowl.

Final Serving – Assenbly

• Stir Macaroni until sauce is smooth (sauce may look loose but will thicken as it cools). Season with salt and pepper to taste. Transfer to warm serving dish and sprinkle panko mixture over top. Serve immediately.