Preheat oven to 200°C / 180°C fan forced. Cook pasta in large saucepan of boiling water, until just tender, adding cauliflower to pan for the last 5 minutes of cooking time. Drain.

Meanwhile, heat half the oil in a large saucepan over medium heat. Cook half the thyme and half the garlic, stirring, for 1 minute or until fragrant. Add flour. Cook, stirring, for 1 minute or until mixture bubbles.

Gradually stir in the milk, whisking constantly until smooth. Bring to the boil. Reduce heat to low. Cook, stirring constantly, for 4-5 minutes or until the sauce thickens. Stir in pasta mixture and 1 cup (90 g) of the cheese until smooth and combined. Season with salt and pepper. Transfer mixture to a baking dish.

Combine breadcrumbs, rosemary, remaining thyme, cheese and oil in a bowl. Scatter over pasta mixture. Bake for 20-25 minutes or until top is golden and crisp. Serve sprinkled with extra thyme leaves if desired.