How to Make It
Preheat the oven to 400°F.
Cut the top 1/4 inch off the garlic, then sprinkle the head of garlic with a pinch of salt and wrap in foil. Roast the garlic in the oven until golden, about 45 minutes. Squeeze the garlic cloves from the skins and reserve.
In a large pot of boiling salted water, cook the pasta until al dente, then drain.
While the pasta is cooking, in a medium saucepan, heat the oil over medium high heat until hot, then whisk in the flour and cook, whisking, until the flour is fragrant, about 4 minutes. Whisk in the milk and 1/2 teaspoon each salt and pepper, then bring to a boil, whisking. Boil until the milk is slightly thickened, about 8 minutes. Remove from the heat and whisk in the cheeses until melted, then whisk in the reserved garlic. Season the sauce with salt and pepper to taste. Toss the pasta together with the sauce and serve.