While your oven preheats to 390°F, whisk together the mustard, honey, olive oil, garlic powder, and a pinch of salt and pepper in a small bowl. The honey will incorporate more smoothly if you whisk it thoroughly with the other wet ingredients. Set the glaze aside until ready to use.

Pat the chicken thighs dry with paper towels, then arrange them in a single layer in a 9x13 inch baking dish or similar size. Season both sides generously with salt and pepper. I find that patting the chicken dry helps it brown better and allows the seasoning to stick more evenly.

Pour the honey mustard glaze from Step 1 over the chicken thighs, using a spoon or brush to coat each piece evenly. Transfer the baking dish to the preheated 390°F oven and bake for 40 minutes, until the chicken is cooked through and the glaze has caramelized into a rich, glossy coating. The chicken should reach an internal temperature of 165°F when a meat thermometer is inserted in the thickest part.