Home » Recipes » Family » Grown Up Entertaining » Onion & Gruyere Tart

225g plain flour 125g butter, cubed 1 British Lion egg, beaten 1 tbsp water 30g Parmesan 500g onions, thinly sliced knob of butter 1 tbsp olive oil 4 large eggs 300ml double cream 150ml milk 200g Gruyere, grated 30g Parmesan, grated a little salt and black pepper <ol> <li>Line a 24-25cm deep round loose bottom tart tin.</li> <li>To make the pastry, put the flour, butter and cheese into a food processor. Whiz until it looks like breadcrumbs. Add the egg and water and whiz until the mixture forms a ball.</li> <li>Roll out on a lightly floured work surface and line the base and sides of the flan tin with the pastry. Set aside to chill in the fridge for 30 to 35 minutes. Prick the base and line with baking beans.</li> <li>Pre-heat the oven to 220C / 425F. Blind bake the pastry for 10 minutes. Remove the beans and bake for another 8 to 10 minutes until lightly golden.Place on a baking sheet.</li> <li>To make the filling. Melt the butter and oil in a frying pan. Add the onions and fry over a medium to high heat for 5 minutes. Cover with a lid and gently simmer for 20 minutes until soft and golden brown. Spread onto the base of the tart.</li> <li>Beat the eggs in a bowl. Add the cream and milk and season. Add the Gruyere cheese, and then pour into the case. Sprinkle with the Parmesan.</li> <li>Reduce the oven to 180C / 350F. Bake for 30 to 35 minutes until lightly golden on top and set in the middle.</li> </ol>