Step 1: Preheat your oven to 400°F (200°C). Pat the chicken thighs very dry with paper towels. This is crucial for crispy skin.
Step 2: Season the chicken thighs generously all over with salt, black pepper, smoked paprika, and onion powder. Make sure to get under the skin slightly.
Step 3: In a large (12-inch or larger) oven-safe skillet (cast iron works best), add the chicken thighs skin-side down. Place over medium-high heat. Cook for 8-10 minutes, or until the skin is deeply golden brown and much of the fat has rendered out into the pan. This rendered fat is the 'schmaltz' that will flavor your potatoes.
Step 4: While the chicken is browning, in a large bowl, combine the potato chunks, cherry tomatoes, olive oil, chopped rosemary, chopped thyme, minced garlic, a pinch of salt, and a good grind of black pepper. Toss to coat everything evenly.
Step 5: Remove the skillet from the heat. Carefully flip the chicken thighs over so they are skin-side up. If there is an excessive amount of rendered fat, you can carefully spoon out a tablespoon or two, leaving enough to coat the bottom of the pan and roast the vegetables.
Step 6: Arrange the seasoned potatoes and tomatoes in the skillet around the chicken thighs, making sure they are in a single layer as much as possible for even roasting. Try to get some of the potatoes directly in contact with the pan for maximum crispiness.
Step 7: Transfer the skillet to the preheated oven. Roast for 30-35 minutes, or until the chicken thighs reach an internal temperature of 165°F (74°C) and the potatoes are tender and golden brown. The tomatoes should be bursting and slightly caramelized.
Step 8: If you want extra crispy skin on the chicken, you can turn on the broiler for the last 2-3 minutes, watching carefully to prevent burning.
Step 9: Remove from the oven. Let the skillet rest for 5 minutes before serving. Garnish with fresh parsley or chives, if desired. Serve the One-Skillet Chicken Thighs with Schmaltz-Roasted Potatoes & Tomatoes directly from the skillet.