01 -
Crank your oven up to 400°F (200°C, or 180°C fan). Cover your biggest baking tray with some parchment.
02 -
Take a sharp knife and cut about 6 thick slices (roughly ¾ inch) from both cauliflowers. Don't stress if bits break off - you can put them back together on the tray later.
03 -
Scatter Parmesan across the parchment-lined tray, then lay your cauliflower slices on top, making sure they don't overlap.
04 -
Combine your oil, salt, pepper, and onion powder in a little bowl. Brush this tasty mix all over the cauliflower pieces.
05 -
Stick the tray in the oven for about 20 minutes, until you can easily poke a fork through the cauliflower.
06 -
Sprinkle each piece with your shredded Gruyere or cheddar and put back in the oven for another 10-15 minutes until the cheese gets all melty and golden.
07 -
Top with some fresh chives and serve immediately while everything's still hot and gooey.