Preheat oven to 200C/180C fan/gas mark 5.
Arrange the red onion quarters on a baking sheet and drizzle over the olive oil and balsamic vinegar. Oven roast the red onion for 15 minutes, until beginning to soften.
Add the Tenderstem® broccoli to the tray with the rosemary sprigs and toss in the tray juices. Season to taste with salt and black pepper, then cook for a further 12-14 minutes and serve.
More ways to cook Tenderstem®