Preheat oven to 425°F. Fill a bowl with ice water.
Bring a large saucepan of water to a boil. Add Brussels sprouts; reduce heat to maintain a lively simmer and cook until just tender when pierced with a skewer, 8 to 10 minutes. Drain the Brussels sprouts and plunge them into the ice bath. Let stand until cool enough to handle, then transfer to a clean kitchen towel and pat dry.
Spread the sprouts on a large rimmed baking sheet. Drizzle with oil and sprinkle with salt and pepper. Toss to coat. Space the sprouts evenly on the pan, then flatten them with the bottom of a mason jar or sturdy glass.
Roast for 10 minutes. Flip the sprouts and top with goat cheese. Return to the oven and bake until the cheese has browned in spots, 3 to 5 minutes more. Drizzle with hot honey. Sprinkle with rosemary, if desired.
