Preheat the oven to 400ºF, then pat the chicken thighs dry with paper towels

Add ½ teaspoon of course salt and all of the fennel seeds to a mortar and pestle. Grind them together until the fennel seeds have broken down a bit and are very fragrant.

Mix the ground seeds with the rest of the salt and the black pepper. Season the chicken thighs all over with spice mixture.

Place the seasoned chicken thighs skin-side down in a large cast iron skillet. The skillet should be room temperature to start, and there is no need to add any oil to the pan.

Place the chicken over medium heat. Resist the urge to meddle in the cooking process for the next 12 minutes or so. Give the chicken skin time to render its fat and become golden brown. Rotate the pan every few minutes to ensure even cooking.

Peel the onion and trim the ends. Cut it into ¼” inch slices, then set aside for now.

Remove the fronds from the fennel bulb. Trim the end off of the bulb, and remove the outermost layer if it seems tough. Slice the bulb into ¼” slices, then add to the pile of onion.

Smash and peel the garlic cloves. Finely chop, along with the fennel fronds until they are well acquainted.

Place the chopped garlic and fronds in a small bowl, then add the vinegar. Drizzle in the olive oil, whisking with a fork, until the mixture resembles a sauce. Season with salt and pepper to taste, set aside.

Use tongs to remove the browned chicken from the pan, and set aside for now.

Add the sliced onion and fennel to the pan. Saute for a few minutes in the rendered chicken fat, until they are slightly softened. Season with salt and pepper.

Pour in the wine, stirring up any of the fond that may be stuck to the bottom of the pan. Beware of splatter.

Add the chicken back to the pan, skin side up, layering over the onion and fennel. Place the skillet in the oven and bake for 15-20 minutes, until the thighs are cooked through.

Remove from the oven and allow the chicken to rest for about 5 minutes, then spoon the fennel frond sauce over top.