Wash and dry all produce. Preheat oven to 475 degrees. Trim and halve Brussels sprouts lengthwise. Peel and halve parsnips lengthwise. Slice into 1/2-inch half-moons. Cut sweet potatoes into 1/2-inch rounds. Halve lemon, then cut one half into wedges.

Divide veggies between two baking sheets. Toss with a large drizzle of olive oil, salt, pepper, and a few sprigs of thyme. Roast about 12 minutes, toss, then continue roasting until golden brown, another 12-13 minutes.

Meanwhile, season chicken on all sides with salt and pepper. Heat a large drizzle of olive oil in a large pan over medium-high heat. Add chicken and cook until browned but not fully cooked through, 3-4 minutes per side.

Finish chicken: Transfer chicken to baking sheets with veggies, and finish cooking until no longer pink in the middle, 5-8 minutes.

Add demi glace, 1 cup water, and a few sprigs of thyme to same pan over medium heat. Bring to a boil, and scrape up any browned bits from bottom of pan. Reduce to a simmer until thickened and reduced by half, 3-5 minutes. Stir in butter, remove from heat, and stir in juice of half a lemon.

Serve: Discard thyme sprigs. Serve chicken and veggies with pan sauce and lemon wedges. Enjoy!