I discovered this one serving size recipe on the Smitten Kitchen website.

Kosher salt
4 ounces (115 grams) dried pasta, such as macaroni or another small twisty shape
2 teaspoons (10 grams) salted or unsalted butter
2 teaspoons (6 grams) all-purpose flour
1/2 cup (125 ml) low-fat or whole milk
Many grinds of black pepper
1/2 cup (1 ounce or 30 grams) finely grated parmesan or pecorino cheese.

Bring a medium pot of water to a boil and add dried pasta. Cook it until firm tender, then drain. Return pot to stove and melt butter in the bottom. Using a spoon or whisk, add flour and mix until it disappears. Add milk, stirring constantly. Season with 1/4 teaspoon salt and black pepper. Bring sauce to a simmer. Cook, stirring, for 1 to 2 minutes. Remove from heat and stir in grated cheese until combined. Add drained pasta, stir to evenly coat.