Place a shelf in the middle of the oven and preheat oven to 450°.
Pat chicken dry with a paper towel and place on a large cutting board. Remove anything from the inner cavity, if needed. Place chicken breast side-down and use kitchen shears to cut along both sides of the back bone to remove it. Flip the chicken over and press down firmly in the center of the breasts to flatten the bird. Cut off wing tips.
Place chicken breast side-up on a large rimmed sheet pan. Rub chicken all over with olive oil, and season generously with salt and pepper. Bake for 30 minutes.
Meanwhile, begin the preparing the rice: In a 12-inch cast iron skillet melt butter over medium heat. Add onion and cook, stirring occasionally, for 3-4 minutes, or until fragrant and starting to soften.
Add carrots, beets, parsnip, sage, rosemary, rice, 1 tsp salt, and ½ tsp pepper. Cook for 1-2 minutes, stirring occasionally.
Stir in sherry or white wine and chicken broth. Bring to a simmer and adjust heat as needed to maintain a gentle simmer.
Remove chicken from oven and carefully transfer with a large, sturdy spatula to the skillet, on top of rice. Pour drippings from the sheet pan over chicken. Place lemon wedges around the chicken.
Place skillet in the oven. Reduce heat to 375°. Bake for 20-30 minutes, or until liquid has mostly absorbed, rice is tender, and chicken is 160-165° in the thickest part of the breast and thigh.
Remove chicken to a cutting board and allow to rest for 5-10 minutes before carving. Mix Parmesan cheese into rice pilaf.
With a chef’s knife cut chicken in half between the breasts. Cut between breasts and thighs to remove the legs. Serve chicken with rice pilaf.