Pour the flour, salt and cold butter into a large bowl or the bowl of your food processor. Mix well and add the cold water a little at a time until the dough is smooth.

Form a ball and flatten it slightly. Cover the dough with cling film and place in the refrigerator while you prepare the rest of the dough (between 15 minutes and 1 hour). Blind bake the shortcrust pastry for 10-15 min in the oven at 180°C (see my post about quiche crust to learn more about blind baking)

Cut the mushrooms into strips. In a large skillet, heat a little olive oil or butter. Add the mushrooms and sauté for 5 minutes on medium-high heat until they are lightly golden brown but not completely cooked. Season with salt and pepper. Add chopped garlic.

Wash the spinach and add it to the mushrooms. Sauté for more 2 minutes on medium heat until it reduces in volume. Set aside.

Roll out shortcrust pastry on a floured work surface using a rolling pin. Form a circle slightly larger than your tart pan. Place the shortcrust pastry on the tart pan greased or covered with parchment paper. Prick the pastry with a fork. Blind bake in the oven at 180°C (fan oven) for 15 minutes.

In a small bowl, mix the eggs, the cream and the finely chopped chives. Add salt and pepper. Whisk lightly. Add the grated Emmental cheese.

Place the mushroom and spinach mixture in the bottom of the pie crust. Pour in the egg mixture. Bake in the oven for 30 minutes at 180°C (fan oven). While the quiche bakes, prepare the side salad.