I picked up a pack of heirloom carrots the other day and wanted to make something to show off their vibrant colours and flavours, and a cheese-topped gratin is always a winner for me. Of course I had to add a little potato or four because I love ’em, and beetroot because their sweet, earthiness goes well with anything.

Yep, the white ones are carrots, not parsnips. Carrots were originally white, with the orange ones being a 17th century selective breeding invention of the patriotic Dutch, or so the BBC says. The purple ones are my favourite, because they are orange inside when you bite into them, but exposure to the air turns the outer layer purple again! Awesome!

Serves 4-6

Ingredients

olive oil
2 medium onions, halved and sliced about 1cm thick
2 large cloves garlic, finely chopped
280g (10 oz) beetroot (2 medium)
280g (10 oz) potatoes (4 smallish)
280g (10 oz) carrots (3 large)
2 tsp fresh thyme leaves
1/2 teaspoon coarse sea salt
1/2 teaspoon freshly ground black pepper
50g (1/2 cup) grated Gruyère
2 tbsp dry breadcrumbs

Directions

Preheat oven to 190°C.

Brush a shallow round baking dish with olive oil and set aside – my dish was 3.5cm (about 1 1/2″) high and 27cm (10 1/2″) across.

Heat one tablespoon of olive oil on medium-low in a skillet. Add the onions and cook for around 15 minutes, until starting to brown. Add the garlic and cook for another 3 minutes. Set aside.

Peel the beets and cut in half crosswise, then slice them, the potatoes and the carrots into 1/2cm (1/5″) slices. Arrange them in the dish, largest on the bottom to smallest on top (for me, this meant potatoes, then beets, then carrots).

Spread the onions over the top of the vegetables and sprinkle with thyme leaves and salt and pepper.

Cover tightly with aluminium foil and bake for about 75 minutes – check for doneness by piercing with a sharp knife.

Remove the foil and sprinkle with cheese, then sprinkle the breadcrumbs over the top of the cheese. Drizzle with 2 teaspoons of olive oil.

Bake uncovered for a further 20 – 25 minutes, until the top has crisped and browned to your liking.

Let stand for 10 minutes before serving.