Step 1: Preheat and Prep the Pan - Preheat your oven to 400 degrees. Grab a 9 by 13 baking dish and place the chicken thighs on one side of the dish. Spread the diced sweet potatoes and halved Brussels sprouts on the other side. Keeping things separated at first helps everything cook evenly.
Step 2: Make the Maple Mustard Sauce - In a small bowl, combine the maple syrup, Dijon mustard, brown sugar, apple cider vinegar, onion powder, and garlic powder. Stir until smooth and well blended. This sauce should smell sweet, tangy, and a little savory all at once.
Step 3: Coat Everything Well - Pour the sauce over the chicken and vegetables. Use a spoon or tongs to toss everything so it is evenly coated. Make sure the chicken thighs get well covered since they are the star of the show.
Step 4: Roast Until Tender - Place the baking dish in the oven and cook for 35 to 45 minutes or until the chicken is cooked through. Every 10 minutes, pull the dish out and baste the chicken and stir the vegetables with the juices at the bottom of the pan. This step makes all the difference for flavor.
Step 5: Broil for Color - During the last five minutes of cooking, turn on the broiler to give the chicken a little extra color. Keep a close eye on it so it browns without burning. This final step adds great texture and visual appeal.
Optional Step: Make a Quick Gravy - If you want to turn those pan juices into a gravy, melt two tablespoons of butter in a skillet over medium high heat. Whisk in two tablespoons of flour until smooth. Carefully pour in all the juices from the baking dish and stir until thickened. Remove from heat and serve alongside the chicken and vegetables.