Bring a large pot of salted water to a boil and cook the elbow noodles according to package instructions. Drain and rinse and wipe out the pot. In a large measuring cup, combine the milk and heavy cream.

Heat the butter in a skillet over medium high. Once melted and frothy, add the flour and use a wooden spoon to incorporate. Cook until smooth and just a touch golden, about 2-3 minutes. Add a ladle of the milk-cream mixture and whisk to thoroughly combine. Continue adding the milk-cream mixture, whisking after each incorporation until there is no more left and the sauce is smooth and creamy.

Reduce heat to medium low. Stir in the harissa paste and whisk until smooth.

Stir in the shredded cheddar cheese and whisk constantly until the cheese is melted and the sauce is smooth. If the sauce seems too thick, add a bit more milk and whisk until smooth. Continue adding milk until desired consistency has been reached.

Taste the sauce and season with a dash of white pepper, a bit of salt, and cayenne powder if you'd like to add more heat.

Add the cooked elbow noodles and stir to combine. Cook over medium low for another minute or two to warm the noodles. Remove from heat.

Divide mac 'n cheese between bowls. Serve with a touch more cayenne powder on top if desired. Enjoy!