For the chicken:
1 tablespoon canola oil
8 bone-in chicken thighs (about 2 to 2 1/2 pounds)
Freshly ground black pepper
1/3 cup maple syrup
1/4 cup Dijon mustard
2 tablespoons whole-grain mustard
1 tablespoon cider vinegar
1 teaspoon soy sauce or tamari
For the broccoli:
1 head broccoli (about 1 1/2 pounds), or 12 ounces broccoli florets
2 tablespoons citrus vinaigrette, plus more as needed
For the chicken: Arrange a rack in the middle of the oven and heat to 400°F. Meanwhile, sear the chicken.
Heat the oil in a cast iron skillet or large ovenproof frying pan (at least 12 inches) over medium-high heat until shimmering. Season the chicken lightly with salt and pepper on all sides. Place half of the chicken skin-side down and sear until just the skin is golden-brown, 6 to 8 minutes. Remove to a large plate skin-side up and repeat with searing the remaining chicken. Meanwhile, make the glaze.
Whisk together the maple syrup, Dijon, whole-grain mustard, vinegar, and soy sauce or tamari in a small bowl; set aside.
When all the chicken is seared and removed to the plate, carefully drain off the grease (no need to wipe out the pan after). Pour half of the glaze into the pan and tilt the pan as needed so it covers the bottom. Return all the chicken to the pan skin-side up. Drizzle the chicken with the remaining glaze, spreading it with the back of a spoon to make sure the skin is evenly coated.
Place the skillet in the oven and bake until the chicken is cooked through and the thickest piece registers 165°F on an instant-read thermometer, about 20 minutes. Meanwhile, make the broccoli.
For the broccoli: Heat a large saucepan of heavily salted water over high heat until boiling. While the water is heating, trim the broccoli (if using the whole head): Cut the florets into 2-inch pieces (save the stems for another use or broccoli slaw).
Add the florets to the water and cook until crisp-tender, 3 to 4 minutes. Drain well and place in a large bowl. Drizzle the vinaigrette over the warm broccoli, season with salt, and toss to combine. Taste and season with more vinaigrette or salt as needed. Serve the broccoli with the chicken and the extra sauce in the skillet.