Peel onion and slice into wedges. Slice fennel bulbs into 1cm slices. Place in small roasting tray. Top with thinly sliced apple wedges.

Microwave butter until melted. Drizzle melted butter over onion and fennel slices. Shake roasting dish a few times to make sure everything gets covered.

Season with salt and freshly ground black pepper. Add a few fennel fronds.

Roast for about 45 minutes or until fennel and onion slices are jammy and caramelised at the bottom.