Cauliflower + Caramelised Onion Tart

A couple of weeks ago I challenged myself to spend more time in the kitchen cooking through a mounting list of recipes and ideas that I have but never seem to get round to doing. So here we are again, this time with cauliflower and caramelised onions.

This is what’s up, cauliflower and cheese was one of my favourite dishes growing up, almost on par with mac n cheese (pasta over vegetables, right?), and whenever confronted with it at the dinner table I would go in solo with no shame. This tart is that cauliflower and cheese but better, and inside pastry. Just try and imagine how dangerous this is then times that by 1000. 

Filled with sweet caramelised onions, roasted cauliflower florets, mascarpone cheese, sour cream, Gruyère and spiked with thyme and black pepper this tart is pure indulgence. And what would a tart like this be if it wasn’t sprinkled with parmesan for that crispy top? A waste of time, that’s what.

Luxurious and comforting all in one go, it’s kind of like wearing grandma’s pearls in a onesie.

Cauliflower + Caramelised Onion Tart | Thyme & Honey

Cauliflower + Caramelised Onion Tart

Makes one 9" tart

Adapted from Smitten Kitchen



250g all-purpose flour

125g very cold unsalted butter, cut into cubes

1 egg yolk

1/2 teaspoon salt

3-4 tablespoons cold water


Olive oil

2 medium cauliflower heads, cut into florets (total of 600g)

2 medium white onions, sliced

1 tablespoon whole grain mustard

2 large eggs

200g mascarpone cheese

120g sour cream

100g Gruyère cheese, grated

A few sprigs of fresh thyme, stalks removed

50g Parmesan cheese, grated



  1. Start with the two main components of the tart, and if you have time then I would even suggest doing this the night before.
  2. Toss the cauliflower florets in 3 tablespoons of olive oil, season with salt and pepper and roast at 220°c for 40 minutes, turning halfway through cooking. Meanwhile cook the onions in a large frying pan with 2 tablespoons of olive oil for around 30 minutes or until deep golden brown and caramelised. If you prepare the cauliflower and onions in advance then store separately in the fridge.
  3. To make the pastry, add the flour, salt and butter to a food processor and pulse until it resembles bread crumbs. Add the egg yolk and water 1 tablespoon at a time, and pulse again until it just comes together. Tip out onto a floured surface, press into a ball and refrigerate for 10 minutes. Once chilled, roll out the pastry to a couple of inches larger than your pie pan.
  4. Flour the pastry well and roll it up over the rolling pin. Unroll and drape it over the pie pan and gently press in the sides. Leave about half an inch or so of pastry hanging over the edges. Refrigerate for 15 minutes while you preheat the oven to 180°c.
  5. After chilling, brush the inside of the pastry with whole grain mustard and layer over the caramelised onions followed by the cauliflower. Whisk together the eggs, mascarpone and sour cream and stir in the grated Gruyère and fresh thyme and season well. Pour the mixture over the tart filling and sprinkle with parmesan. Bake in the oven for 50 minutes and leave to cool for 15 minutes before serving.