Combine 1 Tbsp. salt, 1 tsp. pepper, onion powder, sweet paprika, dried rosemary, sage, and dried thyme in a small bowl.

Pat chicken dry. Use a sharp Paring Knife to remove wishbone. Rub chicken with 1 Tbsp. oil. Season chicken inside and out with spice rub . Slice 1 lemon in half and stuff inside chicken along with half of thyme or rosemary sprigs. Cross legs and use butcher’s twine to tie legs together at end of drumsticks. Place on a Sheet Pan Rack set over a Sheet Pan and let sit at room temperature at least 45 minutes, or up to overnight in fridge (bring to room temperature before cooking).

Prep your vegetables: Peel carrots and/or parsnips and slice into 2” long pieces (halve lengthwise if large). Remove fronds from fennel and reserve. Slice fennel bulb lengthwise into quarters, remove core, and slice into 1” wedges. Slice off top of each head of garlic crosswise to just expose tops of cloves. Peel and halve red onion. Cut into 1” wedges, keeping some root intact so wedges stay together. If potatoes are larger than about 1 ½” in diameter, slice into halves or quarters so that all vegetables are about same size. Toss all vegetables in a medium bowl with 1 Tbsp. oil, 1 tsp. salt, ½ tsp. pepper, and remaining thyme and/or rosemary sprigs.

Position rack in the lower third of oven and preheat to 400F.

In a large Dutch Oven with a lid, heat remaining 2 Tbsp. oil over medium. Take your time to brown chicken skin on all sides until evenly browned, 15–20 minutes total, trying to not tear skin, using 2 spoons or spatulas to turn chicken (you can lean it against inside of Dutch Oven to brown as well). Adjust heat, lowering if necessary, to avoid burning spice rub.

Remove chicken from Pot and transfer to a Sheet Pan or Serving Platter. If spice rub has burned slightly, wipe out Pot to avoid bitterness.

Turn off heat under Pot and add butter, allowing it to melt. Add vegetable mixture and stir, coating vegetables with melted butter. Pour in wine or broth and stir again. Place browned chicken on top, breast side up. Cover Pot with lid, and transfer to oven.

Drizzle sliced bread with olive oil, place on Sheet Pan, and bake in oven with the chicken until browned,  5–7 minutes, then remove and let cool.

Bake chicken 40 minutes. Remove from oven and increase heat to 425F. Baste chicken with juices from Pot and return to oven, uncovered. Bake until chicken is cooked to an internal temperature of 165F, and skin is golden brown, 15–25 minutes more.

Remove chicken from oven and transfer to a cutting board to rest 15 minutes. Remove garlic heads and let cool. Stir vegetable mixture and return to oven, uncovered, to brown while chicken rests.

Squeeze garlic out of heads and onto toasts. Spread to coat and top with a drizzle of olive oil and a sprinkle of flaky salt. Slice remaining lemon into wedges. Carve chicken and serve alongside vegetables and garlic toasts. Top with fennel fronds, a squeeze of lemon, and a sprinkle of flaky salt.