Drizzle a little olive oil in a large saucepan, add the bacon, and bring the pan to medium heat, stir occasionally, about 6-8 minutes. When bacon is brown and crispy, remove it and drain on paper towels. Reserve the bacon fat.

Add the butter and onion to the pan, season with salt and cook for 8-10 minutes, until soft and fragrant. Add the flour and cook, stirring frequently for 4-5 minutes or until mixture looks like wet sand. Slowly whisk in the milk, season with salt, bring to a boil and reduce to a simmer; cook over low heat for 8-10 minutes until the mixture is thicker than heavy cream.

In the meantime, bring a large pot of well salted water to a boil. Add the pasta and cook 1 minute less than instructions on package suggestion. Drain and reserve.

Add the cheeses to the milk mixture and whisk to combine. Add the mustard and a few shakes of Tabasco; taste and adjust the seasoning if needed, adding a little more milk if mixture seems too thick. Stir in the bacon and pasta.

Serve immediately or transfer to a baking dish and reheat in oven at 375° for several minutes.