Servings:
6 servings

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For the Polenta Pastry:

• 115 g quick cook polenta (approx. 4 oz)
• 115 g plain flour (approx. 4 oz)
• 115 g cold butter, cubed (approx. 4 oz)
• 1 large egg, beaten
• 1 tbsp cold water
• A generous pinch of salt

For the Tart Filling:

• 1/2 red onion, thinly sliced
• 5 large cavolo nero leaves, stems removed and roughly chopped
• 150 g pancetta cubes (or diced smoked bacon lardons)
• 1 clove garlic, finely crushed
• 70 g Gruyère cheese, grated
• 30 g blue cheese, crumbled (e.g., Stilton, Gorgonzola, Roquefort)
• 3 large eggs
• 150 ml single cream (or light cream)
• Freshly ground black pepper, to taste
• A drizzle of olive oil, for frying

Preparing the Polenta Pastry:

1. In a spacious mixing bowl, combine the quick cook polenta, plain flour, and a generous pinch of salt. Ensure all dry ingredients are well integrated.
2. Add the cold, cubed butter to the dry mixture. Using your fingertips, gently rub the butter into the flour and polenta until the mixture resembles coarse breadcrumbs. Be careful not to overwork the butter, as warmth from your hands can make the pastry tough.
3. In a separate small bowl, whisk together the beaten egg and cold water. Gradually add this liquid mixture to the breadcrumb mixture, stirring with a knife or your hand until a dough just begins to form. The aim is a slightly wet, pliable dough that’s easy to handle without being sticky. If the dough feels too dry, add an additional teaspoon of cold water at a time until the right consistency is achieved. Avoid adding too much water, as this can lead to a tough crust.
4. Turn the dough out onto a lightly floured surface. Knead it very lightly for just a minute or so until it comes together into a smooth ball. Do not over-knead.
5. Flatten the dough into a disc, wrap it tightly in cling film, and refrigerate for at least 20 minutes (or up to an hour) to allow the gluten to relax and the butter to firm up. This step is crucial for an easy-to-roll and flaky pastry.

Baking the Pastry Shell (Blind Baking):

6. Once chilled, unwrap the pastry and roll it out on a lightly floured surface. Aim for a thickness of about 3-4mm, ensuring it’s large enough to line your chosen tart tin. A rectangular tin provides a lovely presentation, but a 24cm (approx. 9.5-inch) loose-bottomed round tart tin works equally well.
7. Carefully lift the rolled pastry and gently press it into your tart tin, ensuring it fits snugly into the corners and up the sides. Trim any excess pastry from the edges, leaving a slight overhang if desired to prevent shrinkage. Prick the base of the pastry all over with a fork; this prevents air bubbles from forming and ensures an even bake.
8. Preheat your oven to 180°C (350°F / Gas Mark 4).
9. Line the pastry shell with baking parchment and fill it with baking beans, rice, or dried pulses. Blind bake for 20 minutes. This pre-baking step helps create a crisp crust.
10. Remove the tin from the oven, carefully lift out the parchment and baking beans. Brush the base and sides of the pastry with a little extra beaten egg (this creates a seal and prevents a soggy bottom). Return the pastry to the oven for another 5 minutes to crisp up and become lightly golden. Remove from the oven and set aside.

Preparing the Flavorful Filling:

11. While the pastry is blind baking, begin preparing the tart filling. Heat a drizzle of olive oil in a frying pan over medium heat. Add the thinly sliced red onion and cook gently until it has softened and caramelized slightly, about 5-7 minutes.
12. Add the chopped cavolo nero leaves to the pan with the onions. Sauté for just 1-2 minutes until they begin to wilt but still retain a vibrant green color. Transfer the onion and cavolo nero mixture to a bowl and set aside.
13. In the same pan, fry the pancetta cubes over medium-high heat until they are beautifully crispy and golden brown. Drain off any excess fat.
14. Add the crushed garlic clove to the crispy pancetta and cook for just 30 seconds until fragrant, being careful not to burn it. Remove from the heat.
15. Evenly spread the cooked onion, cavolo nero, pancetta, and garlic mixture over the base of the pre-baked tart shell.
16. Crumble the blue cheese evenly over the filling, then sprinkle with the grated Gruyère cheese. Finish with a generous grind of fresh black pepper.
17. In a clean bowl, whisk together the 3 large eggs and the single cream until well combined. This is your rich custard base.
18. Carefully pour the egg and cream mixture over the filling in the tart shell, ensuring it distributes evenly amongst the ingredients. If it looks like you need a touch more liquid to just cover the filling, you can whisk a little extra cream with an egg if necessary, but 150ml usually suffices.

Final Bake and Serving:

19. Carefully transfer the filled tart to the preheated oven (still at 180°C / 350°F / Gas Mark 4). Bake for approximately 30-35 minutes, or until the filling is set (it shouldn’t wobble too much in the center when gently shaken) and the top is a beautiful golden brown.
20. Once baked, remove the tart from the oven and let it cool in the tin for about 10 minutes before carefully releasing it.
21. For the best flavor and texture, this tart is wonderfully versatile and can be enjoyed at room temperature. It allows the complex flavors of the red onion, salty pancetta, pungent blue cheese, and earthy cavolo nero to truly sing. It’s equally delicious served warm, but avoid serving it piping hot straight from the oven, as the custard needs a moment to set properly.