Gluten-free quiche

Name: Gluten-free quiche
Prep time: 1 h
Cook time: 1 h
Total time: 2 h
Cuisine: European, Mediterranean, French
Ingredients: 250g/9oz gluten-free plain flour; 125g/4½oz unsalted butter, chilled and diced; 2 tbsp finely grated Parmesan, or alternative vegetarian hard cheese; 1 tbsp poppy seeds; 4–5 tbsp ice-cold water; 1 tsp white wine or cider vinegar; 1 egg, white only, beaten (reserve the yolk for the filling); salt and freshly ground black pepper; 2 tbsp olive oil; 1 onion, thinly sliced; 1 leek, thinly sliced; 200g/7oz smoked bacon bits or lardons; 5 eggs, 4 whole eggs and 1 yolk (plus the yolk reserved from sealing the pastry); 375ml/13fl oz double cream; 2 tbsp snipped chives or chopped parsley; 75g/2¾oz Cheddar or gruyère, grated; 100g/3½oz frozen peas, defrosted