Bring a large pot of salted water to a boil and cook pasta until al dente; drain and set aside.
In a large saucepan, melt the butter over medium heat.
Whisk in the flour until the mixture is smooth and bubbly.
Cook the roux for two minutes to eliminate the raw flour taste.
Slowly pour in the room-temperature milk while whisking constantly to avoid lumps.
Continue cooking and whisking until the sauce thickens to a velvet consistency.
Remove from heat and stir in the freshly grated white cheddar until fully melted and smooth.
Season the cheese sauce with sea salt and white pepper to taste.
Add the cooked pasta to the sauce and toss until evenly coated.
Serve immediately while warm and creamy.