Simon Rimmer makes Cheese and onion tart for The Vamps on Daily Brunch.
The ingredients are: 300g plain flour, plus extra for dusting, 175g unsalted butter, 125g for the pastry, and 50g for the filling, 5 free-range eggs, 1 for the pastry, 1 beaten to glaze and 3 for the filling, 7 red onions, 6 peeled and sliced for the filling and 1 finely diced for the salad,2 tbsp milk, to bind (if needed), 200ml double cream, 75g gruyere cheese, grated, 1 tbsp fresh thyme leaves, 6 tomatoes, chopped, 1 tsp dijon mustard, 1 tsp white wine vinegar and 3 tbsp olive oil.
To prepare the tart pastry, place the flour, butter, and egg into a food processor and pulse to combine. If necessary, add a little milk to help bring the mixture together.
Preheat the oven to 200˚C/400˚F/Gas 6.
Turn the dough out onto a floured work surface and roll out until large enough to line a 20cm tart tin. Carefully lift into the tin, then place into the fridge to chill for an hour.
Fill the tart case with a sheet of greaseproof paper weighed down with baking beans or rice. Bake the tart case blind in the oven for 15-20 minutes.
Remove the paper and beans and brush the pastry all over with beaten egg. Return to the oven for a further five minutes, until golden-brown. Remove from the oven and turn the oven temperature down to 180˚C/350˚F/Gas 4.
Meanwhile, for the gruyère and red onion tart, heat the butter in a frying pan until foaming and fry the onions for 8-10 minutes, or until completely soft.
Whisk the eggs and cream together and stir in the cooked onions, cheese and thyme. Season, to taste, with salt and freshly ground black pepper
Spoon the onion mixture into the pastry shell and bake for 20-25 minutes, or until the filling has set. Remove from the oven and set aside to cool slightly.
Make the dressing by whisking together the mustard, vinegar and olive oil, season with salt and pepper and use to dress the tomato and onion
To serve, slice the tart into wedges and serve the salad on the side.