Tip:Depending on the size and shape of the pasta, volume measures and cooking times vary. Go with the weight measurement and adjust the cooking time accordingly.
Whisking flour into sour cream keeps the cream from separating during cooking.
Turn this into a main dish by adding steamed peas and diced ham or prosciutto.
Bring a large pot of water to a boil over high heat. Once boiling, add the pasta and 1 Tbs. of the salt. Cook, stirring occasionally, until the pasta is just tender, about 8-min. or according to the package directions. Meanwhile, whisk the sour cream and milk together in a small bowl. Add the flour, stir until smooth, and set aside.
Drain the pasta and shake the colander to remove the excess water. Return the cooked pasta to the pot and pour in the sour cream mixture. Set the pot over medium-low heat and stir until the ingredients are well combined and the sauce is thickened and coats the pasta, about 1 min. Toss in the cheese, the remaining 3/4-tsp. salt, the pepper, and the chives (if using) and stir until well blended. Taste and adjust the seasonings if necessary. Garnish with more Parmesan and chives, if you like. Serve immediately.