Arrange the seasoned thighs in a single layer on a rimmed baking dish, such as a 9 X 13-inch baking dish. If there's some residual oil and spice mixture in the bowl, brush it on the chicken pieces.
Bake uncovered until the thighs are cooked through, juices run clear, and an instant-read thermometer inserted into the middle of the largest thigh reaches a minimum of 165ºF (see notes below). In my oven, this takes about 30 minutes.
Serve immediately.
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Notes
Dark chicken meat, including thighs, is safe to eat at 165°F, but it becomes more tender and flavorful when cooked to around 180°F. While 165°F ensures doneness, the extra heat helps break down connective tissue, resulting in a juicier texture. For best results, remove the thighs from the oven at about 175°F and let them rest for 5 minutes. Carryover heat will bring them to around 180°F.
If you buy them in pre-packaged trays at the supermarket, boneless, skinless chicken thighs come in various sizes. It's OK to bake them all together until the biggest ones are cooked through. The small ones will still be juicy and delicious!
You can trim the fat, but I don't. Most of it melts away during baking, and what remains is delicious. The fat also helps protect the chicken from drying out in the oven.
Seasonings, especially salt, are guidelines. Adjust to taste. However, the smoked paprika is an important ingredient that adds great flavor. I highly recommend using it.
A few readers have mentioned over the years that although the chicken was delicious, it didn't brown the way mine does. A few things can affect how browned the chicken gets. Ovens vary, and sometimes the thighs release extra moisture and end up steaming instead of baking. If this happens to you, here's my advice for next time: Make sure to pat the chicken thighs very dry before seasoning, give them plenty of space on the pan, and - if the pan is broiler-safe - finish with a quick broil. Doubling the paprika also helps deepen both color and flavor. Even with all that, if your chicken has been "enhanced" (injected with saline or broth), it'll naturally release more liquid as it cooks. That extra moisture makes browning difficult, especially with skinless pieces. Even a hot oven can only do so much against that.
You can keep the leftovers in an airtight container in the fridge for 3-4 days. I usually shred them and add them, cold, to a salad. If you'd like to reheat them, it's best to do so gently, in the microwave, covered, at 50% power. You can also reheat them in a 350°F oven until heated through. Be gentle - the chicken will dry out if you reheat the leftovers too aggressively, especially in the microwave.
Once cool, the leftovers can be frozen in a freezer-safe container for up to three months. Thaw them overnight in the fridge before reheating.