Combine water, salt, and butter. For best results, do not add milk until step 3.
Heat to a boil, remove from heat.
Add cold milk; stir in potato flakes gently and let stand until moist. Whip lightly with a fork and serve.
Combine the cream and milk in a saucepan then heat to a simmer over medium-high heat. Whisk in the shredded cheese and turn the heat to low.
Continue to stir until the cheese is completely melted. Once melted, remove from heat and stir in salt.
TIP: Keep a little hot water handy as this can help adjust the consistency of your cheese sauce if it gets too thick.
To serve, scoop some mashed potatoes in a bowl and ladle 2 ounces (1/4 cup) cheese sauce on top.
Choose any toppings you'd like to garnish the top: crumbled bacon, grilled chicken, sauteed mushrooms, artichoke hearts, sundried tomatoes, steamed broccoli, canned olives, fresh herbs, sour cream, green onions, etc.