Step 1: Preheat and Prepare

1. Preheat your oven to 400°F (200°C).

2. Line a large, rimmed baking sheet with parchment paper for easy cleanup.

Step 2: Make the Sauce

1. In a small bowl, whisk together the olive oil, maple syrup, Dijon mustard, fresh thyme, garlic powder, kosher salt, and black pepper until well combined.

Step 3: Toss the Vegetables

1. In a large mixing bowl, combine the cubed sweet potatoes, halved Brussels sprouts, and red onion wedges.

2. Pour about two-thirds of the prepared sauce over the vegetables and toss thoroughly until every piece is evenly coated.

Step 4: The First Roast

1. Spread the coated vegetables onto the prepared baking sheet in a single, even layer. It’s important not to crowd the pan, as this will cause the vegetables to steam instead of roast. Use two pans if necessary.

2. Roast for 20-25 minutes, until the sweet potatoes are beginning to soften.

Step 5: Add the Sausage and Apple

1. While the vegetables are roasting, place the sliced sausage and chopped apple in the now-empty mixing bowl. Add the remaining one-third of the sauce and toss to coat.

2. Remove the baking sheet from the oven. Add the coated sausage and apple to the pan, nestling them amongst the vegetables.

Step 6: The Final Roast

1. Return the baking sheet to the oven and roast for another 15-20 minutes, or until the sweet potatoes are tender and caramelized, the Brussels sprouts are crispy on the edges, and the sausage is heated through and nicely browned.

Step 7: Garnish and Serve

1. Remove the sheet pan from the oven.

2. If desired, sprinkle with fresh chopped parsley for a burst of color and freshness.

3. Serve immediately, directly from the pan or transferred to a platter.