Add the potatoes to a large pot over medium high heat with enough water to fully cover them. Add salt (I used 2 Tablespoons but adjust to taste). Cook for about 20-25 minutes. Potatoes should be tender but not falling apart.
5 Russet potatoes, 2 tablespoons salt
While the potatoes cook, in a heavy bottomed pan, melt the butter over medium-high heat. Add the paprika, garlic powder and white pepper and cook for 30 seconds
3 Tablespoons Unsalted butter, 1 teaspoon Smoked paprika, 1 teaspoon Garlic powder, 1 teaspoon White pepper, 1 teaspoon Salt
Add the flour and whisk until fully incorporated and you form a paste.
3 Tablespoons All purpose flour
Add the evaporated milk and continue whisking until the sauce starts bubbling.
12 Ounces Evaporated milk
Lower the heat to medium-low heat and slowly add the heavy whipping cream.
2 Cups Heavy whipping cream
In a bowl combine all the shredded cheese and divide the mixture in half. You will use half for the cheese sauce and half to layer on top when baking the Mac and cheese.
1 Lb Mozzarella (16 OZ), 1 Lb Colby Jack (16 OZ), ½ Lb Sharp cheddar (8 OZ)
Add a handful of the cheese to the sauce and whisk vigorously until fully incorporated. Do not add more cheese until the sauce is smooth and all the previous cheese you added has melted.
The sauce should take about 20 minutes to make. This will ensure that the flour is cooked and the cheese melts smoothly.
Once you have added all the cheese to the sauce, add dijon mustard and stir well to combine.
1 Tablespoon Dijon mustard
Place the oven rack in the center and pre heat your oven to 375°F.
Use a 9x13 baking dish and add layer of potatoes, add some of the cheese sauce and top with the some of the reserved shredded cheese.
Repeat the process of layering potatoes, cheese sauce and shredded cheese until the casserole is full. Your last layer should be cheese.
Cover with aluminum foil and bake at 375°F for about 25 minutes. Bake uncovered for 10 minutes until all the cheese on top has melted and is slightly browned.
If you want a golden brown top, broil on low for about 1 to 2 minutes. Keep and eye on the Mac and cheese as broiling can quickly burn the top.
Let the potatoes rest for about 10 minutes before serving.