Start by mixing the dried thyme or rosemary, onion powder, garlic powder, paprika, salt, and pepper in a small bowl. Rub this seasoning blend generously over both sides of the chicken thighs. This step only takes a minute, but it builds so much flavor into the chicken before it ever touches the pan.
Heat the olive oil in a large skillet over medium heat. Add the seasoned chicken thighs and cook for about 5 minutes on the first side. Flip and cook another 6 to 8 minutes, until the chicken is golden and cooked through. Remove it from the skillet and set it aside on a plate.
In the same skillet, add the minced garlic and cook for about 20 seconds until fragrant. Slowly pour in the apple cider, then whisk in the dijon mustard. Drop in the rosemary or thyme sprig and let everything simmer for about 8 minutes, until the sauce reduces and thickens slightly.
Whisk the butter into the reduced sauce a little at a time until it melts completely and the glaze turns glossy. Taste it and adjust the salt and pepper as needed. This is the step that really transforms the sauce from thin to luxurious.
Add the chicken thighs back into the skillet, spooning the glaze over them as they warm through for about 2 minutes. Remove from the heat, garnish with fresh parsley, and serve while everything is still warm and glossy.