Tartiflette au champignons - Untested

https://experimentalmouffette.blogspot.com/2024/05/tartiflette-de-pommes-de-terre-au.html

https://www.quiveutdufromage.com/r-tartiflette-vegetarienne

https://freethepickle.fr/2021/09/29/tartiflette-vegetarienne-aux-champignons/#recipe

0 - It's been a joy to experiment with the traditional version with lardons that I thought it would be nice to share with my vegetarian brethren, so I'm experimenting with the base recipe and working out ways of substituting for the smoky meatiness of the bacon. First thoughts are with mushrooms and soy sauce.

Pie dough divided in 2 : 1¼ cups flour, ¼ teaspoon salt, 5oz/143g butter, 4 Tbsps water

2 Tbsps. olive oil

3 large onions (30oz/855gr), sliced thin

300g button mushrooms, caps quartered (stems removed and finely minced)

3 cloves garlic, finely minced

1 branch rosemary, leafed and minced

1 Tbsp soy sauce

750g to 1 kg (1.8 to 2lbs) potatoes, peeled and sliced thin

250 g Gruyere, sliced thin or grated. (OR TRY A SOFT REBLOCHON-STYLE CHEESE)

1 egg, whisked

Salt and pepper

1. Start with the pie dough to give it a chance to thoroughly rest, covered, in the refrigerator while you cook the onion and mushrooms.
2. Heat the oil in a wide pan and slowly brown the onion and mushrooms in the fat. 
3. When the onions are perfectly soft and browning, add the garlic, the herbs and the soy. Cook for another couple of minutes. Set aside.
4. Divide the dough into two balls. Roll out first to cover the bottom of the pie plate and return all the dough to the refrigerator to chill for 15 minutes.
5. Preheat the oven to 410°F.
6. Once the dough has chilled, spread half the potato in an overlapping pattern in the covered pie plate. 
7. Sprinkle with salt and pepper.
8. Layer all of the cooked onion on top, followed by lardons, and then the cheese.
9. The remaining potatoes go on top in the same overlapping pattern (it'll show through the pastry and be very pretty). 
10. Sprinkle over with more salt and pepper.
11. Wet the edges of the pie shell and drape the remaining rolled out pie dough on top. Pinch the edges securely.
12. Cut the top for vents and brush the top of the pie with the beaten egg.
13. Bake in two stages, the first for 30 minutes. Check it and if it's brown enough, cover with aluminum paper and bake another 20 to 30 minutes. If it's not brown enough, leave uncovered and check after 15 minutes.