Melt butter in a heavy bottomed sauce pan over medium heat. Add garlic, red pepper flakes, and pinch of salt and cook for 2 minutes or until softened but not browned.
Whisk in flour and let the roux cook for a few minutes or until the flour taste has cooked out. Whisk in milk, then let simmer until thick. Slowly add in heavy cream then turn the heat to medium-low. Let simmer for about 10 minutes until sauce has thickened and has slightly reduced.
Now whisk gouda cheese, little by little. Once it’s melted, whisk in half the cheddar and continue to stir until the sauce is smooth and creamy. Be sure to reserve the other half of cheddar. Stir in the the hot sauce, mustard, 1/2 tsp salt and stir. Season with more salt if needed.
Mix in the pasta and pour into a greased baking dish. Top with the remaining smoked cheddar and place under the broiler for 7 to 10 minutes or until the top is golden brown. Remove from broiler and let rest for 5 minutes before serving.