Preheat your oven to 450 degrees Fahrenheit so it's fully hot by the time your chicken goes in. Pat the chicken thighs dry with a paper towel, then rub them all over with olive oil. Generously season both sides with salt and pepper.
Place the seasoned chicken thighs in a single layer inside your baking dish, skin-side up. Giving each piece a little breathing room helps the skin crisp instead of steaming against its neighbors. Avoid overcrowding the pan if you can.
In a small bowl, whisk together the beer, brown sugar, and garlic powder if you're using it. Stir until the sugar has mostly dissolved into the beer. This forms the braising liquid that keeps the chicken from drying out.
Pour the beer mixture around the chicken, being careful not to pour it directly over the tops so the skin stays exposed. Slide the dish into the oven uncovered and bake for about 30 minutes, or until a thermometer reads 165 degrees Fahrenheit.
Once out of the oven, let the chicken rest for about 5 minutes before serving. This gives the juices time to settle back into the meat instead of spilling out the moment you cut into it.