Step 1: Prepare the Pastry

• In a bowl, mix the flour and salt. Add the cold diced butter and rub it into the flour with your fingertips until the mixture resembles breadcrumbs.
• Gradually add cold water, a tablespoon at a time, and mix until the dough comes together.
• Shape into a disc, wrap in cling film, and refrigerate for 30 minutes.

Step 2: Roll Out and Blind Bake the Pastry

• Preheat your oven to 200°C (180°C fan) or 400°F.
• Roll out the chilled pastry on a lightly floured surface and line a 23cm tart tin.
• Prick the base with a fork, line with parchment paper, and fill with baking beans.
• Bake for 15 minutes, then remove the paper and beans and bake for another 5 minutes until lightly golden.

Step 3: Sauté the Mushrooms

• Heat olive oil or butter in a pan over medium heat.
• Add onions and cook for 3 minutes until soft. Stir in garlic and cook for another 1 minute.
• Add the mushrooms and thyme, cooking for 5 minutes until the moisture evaporates.
• Season with salt and black pepper, then set aside to cool slightly.

Step 4: Prepare the Egg Custard

• In a mixing bowl, whisk together the eggs, cream, milk, grated cheese, and nutmeg until smooth.
• Season with a little salt and pepper.

Step 5: Assemble the Quiche

• Spread the sautéed mushroom mixture evenly over the pre-baked pastry case.
• Pour the egg custard over the mushrooms, ensuring an even distribution.

Step 6: Bake the Quiche

• Reduce oven temperature to 180°C (160°C fan) or 350°F.
• Bake for 25-30 minutes, or until the quiche is golden and set in the center.

Step 7: Cool and Serve

• Allow the quiche to cool slightly before slicing. Serve warm or at room temperature with a fresh salad or steamed vegetables.