Closed pie with cheese and potatoes

Ingredients:

Chopped dough

• 3.5 cups flour + extra for work
• 1 tbsp. sugar
• 1 teaspoon fine salt
• 330 g butter, diced (keep in the freezer)
• 1 tbsp white or apple cider vinegar

Filling

• 4 tbsp. l. olive oil
• 1 large onion, thinly sliced
• 4 large red potatoes (0.7 kg), unpeeled
• 2 Gala apples, peeled
• 2 sprigs fresh thyme, leaves picked
• 3 tbsp. breadcrumbs
• 150 g mortadella or ham, thinly sliced
• 280 g white cheddar, grated
• Heavy cream to frost the pie

Preparation:

1. Knead the dough. In a food processor, combine the flour, sugar, and salt. Add 110g of butter and pulse until combined. Add the remaining 220g of butter and pulse three times, or until the mixture resembles coarse meal. Add the vinegar, then gradually pour 1/3 cup of ice water into the top chute, pulse four times until combined. Pinch the dough between your fingers. If it doesn't hold together, add another 2 tbsp of ice water and pulse two more times (the dough should still be crumbly). Turn it out onto a clean surface and form into a ball. Divide in half, wrap in plastic wrap, and flatten into two 2.5cm-thick rectangles. Refrigerate the dough for at least 1 hour or up to 2 days.
2. Prepare the filling. Heat 2 tablespoons of olive oil in a skillet over medium heat. Add the onion and cook for 5-7 minutes, season with salt, and let cool. Slice the potatoes and apples very thinly; toss in a bowl with the thyme, the remaining 2 tablespoons of olive oil, and season with salt and pepper to taste.
3. Line an 8x8 inch (20x20cm) square baking pan with foil, allowing a 3/4 inch (2cm) overhang on all sides. On a floured surface, roll out one piece of dough into a 12 inch (30cm) square and approximately 1/4 inch (0.3cm) thick. Transfer to the prepared pan, aligning the dough around the edges and corners; do not trim. Dust the dough. breadcrumbs and add the onion. Place the mortadella on top, then sprinkle with about a third of the grated cheese. Next, arrange half the potatoes and half the apples in a single layer; season with salt and pepper to taste, then sprinkle with another third of the cheese. Top with the remaining potatoes and apples. Season with salt and pepper again and sprinkle with grated cheese.
4. Roll out the remaining dough into a 30 cm square and place it on top of the filling. Press down the overhanging edges of the top and bottom layers, then fold the dough under and press it to create a 2 cm high border. Use a knife to make slits in the top layer to allow steam to escape. Refrigerate for 30 minutes. Meanwhile, preheat the oven to 220°C.
5. Bake the pie until golden brown, about 30 minutes. Then reduce the oven temperature to 200°C, brush the crust with whipped cream, and continue baking until crisp, about 35 minutes more. Cool the pie for 25 minutes, then remove from the pan and slice.