Heat the oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish.
Cut the sweet onion into rings and pull the rings apart. Spread them over the bottom of the dish.
Place the 6 chicken thighs over the onions in one layer, with the skin facing up. Do not stack the pieces.
Spoon 1 cup of Russian dressing over the chicken. Spread it over the skin of each thigh.
Bake uncovered for about 45 to 50 minutes. Check the thickest part of the chicken with a meat thermometer, keeping the tip away from the bone. It needs to reach at least 165°F (74°C). Large thighs may need more time.
Take the dish out of the oven and let the chicken rest for about 5 minutes.
Serve one chicken thigh with some soft onions and a spoonful of the sauce from the dish.
Notes
The cooking time is for bone-in, skin-on chicken thighs. Use a thermometer to check that the thickest part reaches at least 165°F (74°C).If the tops get too dark before the chicken is done, loosely cover the dish with foil and keep baking.The sauce will be thinner than gravy. Spoon it over the chicken, rice, potatoes or noodles.