For the Filling
- 3 tbsp olive oil
- 2 large onions, halved and finely sliced
- 1 garlic clove, crushed
- 2 tbsp Dijon mustard
- 1/2 cup (100g) Gruyere cheese, grated
- 1/4 cup (50g) Grana Padano, grated
- 1 & 2/3 cup (300g) cherry tomatoes, halved (use a variety of shapes and colors, if you like)
For the Pastry
- 2 & 1/2 cups (350g) all purpose flour
- 5 fl oz (150ml) olive oil
- 1 tsp salt
- Cold water
To make the pastry, mix the flour with 1 tsp salt then stir in the olive oil and just enough water so it comes together as a dough (you’ll need about 4-5 tbsp). Roll out the pastry between 2 sheets of baking paper until it’s large enough to line an 11 inch round tart pan. Trim the edge and chill while you make the filling.
Heat 3 tbsp olive oil in a large pan, add the onions and a good pinch of salt. Sauté very gently over medium-low heat for 20-30 minutes or until meltingly soft and golden. Add the garlic and cook for another couple of minutes. Cool and mix in the mustard and cheeses.
Heat the oven to 350 degrees F. Bake the tart shell for 20 minutes then take out and cool.
Spread the cheesy onions over the base of the tart. Place the tomatoes on top in a single layer, cut-side up, and season with salt and pepper. Put the tart back in the oven for another 20-25 minutes or until the pastry is crisp and the tomatoes are slightly golden. Serve just-warm.
Adapted from Olive Magazine.