Bring a large pot of salted water to a boil and cook the pasta until just tender, following the package instructions.
While the pasta cooks, melt the butter in a heavy saucepan over medium heat. Add minced garlic and a pinch of salt, cooking gently for 2 minutes until fragrant and softened without browning.
Stir in the flour and allow the mixture to cook for 1-2 minutes, helping to get rid of the raw flour flavor.
Gradually whisk in the room temperature milk and add a few pinches of salt, then reduce the heat to medium-low.
Let the milk mixture simmer gently for about 5 to 10 minutes, stirring occasionally until it thickens and slightly reduces.
Slowly add the shredded gouda cheeses one cup at a time, whisking continuously until the sauce becomes smooth and creamy.
Stir in the Dijon mustard and adjust seasoning with salt and pepper to your taste.
Drain the pasta and fold it into the cheese sauce, giving it a good mix. Adjust seasoning with salt and pepper as needed before serving.
