Savory Apple, Cheddar, and Potato Lattice Pie

Prepare the cheesy pastry: In a large bowl, mix 300g of plain flour with 70g of grated cheddar and a pinch of salt. Rub in 150g of cubed cold butter using your fingertips until the mixture looks like fine breadcrumbs. Stir in 4-5 tablespoons of cold water and bring the mixture together into a smooth dough. Wrap in plastic wrap and chill in the refrigerator for 30 minutes.

Start the filling: Melt 30g of salted butter with 1 tablespoon of vegetable oil in a medium saucepan over medium heat. Add the sliced onions and cook for 10-15 minutes, stirring occasionally, until soft and caramelized. Add the thyme leaves and cook for another minute. Stir in 30g of flour to form a paste.

Finish the sauce: Gradually pour in the vegetable stock, whisking constantly to prevent lumps. Bring the sauce to a simmer and cook for 10 minutes until thickened. Stir in the wholegrain mustard and white wine vinegar, then remove from heat.

Prepare the vegetables: While the sauce simmers, boil the potato chunks in a large pan of water for 4-5 minutes until just tender but still firm. Drain well. Fold the potatoes, chopped apples, and 150g of grated mature cheddar into the onion sauce. Season with salt and pepper to taste. Preheat your oven to 200°C (180°C fan/gas 6).