Heat a large skillet to medium heat with the olive oil and flour. Whisk occasionally until the flour combines with the oil and just slightly browns. Keep whisking and slowly stream in the milk. Increase the heat to bring the sauce to a bubble, then add the cheese. Stir to melt the cheese and taste; add salt and pepper to your preference.

Combine the pasta, white sauce, garlic, scallion, spinach, and artichokes in a large bowl or the same pot you used to boil the pasta. Taste the mixture, and add more salt an pepper if needed. Splash in a bit more milk if you'd like a saucier mac.

To serve right away, bake at 425F for 15-20 minutes until the top browns.

To serve in a few days or later that day, keep in the fridge, then put the mac and cheese in a cold oven, set oven to 350F. Let oven and mac come to temperature together, then continue cooking for 20 more minutes until bubbly and hot.

To freeze, cover with plastic wrap then tin foil before freezing. Thaw on the counter for a few hours before baking, then uncover and bake as directed above.