Thyme Onion and Gruyere Tart Recipe

Thyme-Onion- Gruyere-Tart
Thyme Onion and Gruyere Tart Recipe. Elaine Lemm
    2 hrs 20 mins
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You can’t beat a tart when looking for a straightforward and delicious lunch or supper dish. There is something so comforting to see one on the plate especially with a crisp salad on the side. There are many variations on this Thyme, Onion and Gruyere Tart Recipe which essentially is a cheese and onion flan with the addition of thyme which works so well with the other filling ingredients.

This recipe is from Simon Hopkinson's famous book, The Vegetarian Option. 

What You'll Need

  •      ​
  • For the Pastry
  • 65g (1 1/3 oz) cold butter, cut into cubes
  • 100g (3 ½ oz) plain flour
  • Pinch salt
  • 1 - 2 tbsp iced water      ​​​​​
  • For the Filling    
  • 55g (2 oz) butter
  • 750g (26 oz) white onions, peeled and very thinly sliced
  • 1 large egg
  • 2 large egg yolks
  • 200ml (3/4 cup) double cream  
  • 2 teaspoon Dijon mustard   
  • 1 teaspoon thyme leaves
  • Salt and freshly ground white pepper  
  • 60g (1 1/3 oz)  Gruyere, freshly grated
  • Freshly grated nutmeg

How to Make It

  • To make the pastry, briefly process the butter, flour and salt together in a food processor until the mixture resembles fine breadcrumbs. Now tip into a large roomy bowl and gently mix in the water with cool hands or table knife until well amalgamated. Knead the dough lightly, then put into a plastic bag and chill in the fridge for at least 1 hour before rolling.
  • For the filling, melt the butter in a wide, shallow pan. Tip in the onions and very gently sweat over a moderate heat for at least 40 minutes, or as long as 1 hour, until pale golden and completely soft. Cool
  • Meanwhile, preheat the oven to 180°C/ gas mark 4, and place a flat baking sheet inside to heat (it will help the base of the tart to cook thoroughly).
  • Roll out the pastry on a lightly floured surface as thinly as you dare, then use to line a 20cm tart tin, 3 cm deep. Prick the base with a fork. Line the pastry case with foil and dried beans, slide onto the hot baking sheet and bake 'blind' for about 15 - 20 minutes. Remove the foil and beans and return the pastry case to the oven for a further 10 minutes or so, until it is golden, crisp and well cooked through, particularly the base.
  • Mix the egg, egg yolks, cream, mustard and thyme leaves. Carefully mix in the onions, season and pile the mixture into the pastry case. Sprinkle the Gruyere over the surface and generously grate over some nutmeg. Bake in the oven for about 45 minutes, or until the filling is a rich golden colour and just firm to the touch. Leave to stand for 10 minutes before eating.