Place a greased sheet pan in the oven, and heat to 450°F.

Place the Brussels sprouts in a large mixing bowl. Drizzle the olive oil over the Brussels sprouts and season with salt and pepper, to taste. Toss to coat.

Carefully spoon the Brussels sprouts onto the hot sheet pan and quickly spread them out so they have some space to crisp up. Bake for 20-25 minutes, tossing halfway through, until the sprouts are tender and crisp on the edges.

While the sprouts are roasting, make the glaze. In a small saucepan, combine the hot honey, Dijon mustard, apple cider vinegar, garlic, rosemary, butter, and red pepper flakes.

Cook the glaze on the stovetop over medium heat, stirring often, until the butter is melted and the glaze is combined. Bring to a simmer and cook for 5-6 minutes until the glaze is slightly thickened.

Immediately pour the glaze into a bowl and let it cool for a few minutes to thicken slightly.

Once the sprouts are roasted, spoon them onto a serving dish. Toss with about half of the hot honey glaze. Taste, and add more glaze if desired. Garnish with the toasted hazelnuts and serve immediately.