Caramalised onion and broccoli quiche - Gluten-Free Heaven

Ingredients

• 375 g gluten-free flour blend
• 1 tsp caster sugar
• 1½ tsp xanthan gum
• ½ tsp salt
• 250 g unsalted butter (cut into 1cm cubes, chilled)
• 150 g cold water
• ½ quantity savoury flaky all-butter pie crust
• 3 tbsp olive oil
• 3 red onions (thinly sliced)
• 1 broccoli head (cut into bite-sized florets (about 250g prepared weight))
• 100g cheddar cheese
• 6 free-range eggs (at room temperature )
• 120 g whole milk (at room temperature )
• salt and freshly ground black pepper