Preheat oven to 400 degrees Fahrenheit. Line a baking sheet with a baking mat or parchment paper. Set aside.
Put a cup of water with ice cubes in the freezer.
Add flour, sugar, salt, parsley, and thyme to the food processor. Pulse.
Add solid butter and pulse until there are pea-sized pieces of butter.
Add ice water 1 Tablespoon at a time until dough-like consistency (it took me about 5 Tablespoons).
Using a rubber spatula, pour the dough on a sheet of plastic wrap. Wrap the dough into a ball and place in the fridge for 30 minutes to rest.
Remove dough from fridge and place on a lightly floured countertop. Using a rolling pin, roll out into 1/8" thick, 8-10" diameter circle. Transfer to lined baking sheet.
Make the Filling:
Melt butter in a large pan over medium heat. Add onions and sautee until soft and translucent (about 5 minutes).
Add garlic and cook until fragrant (about 1 minute).
Add mushrooms and cook until soft (about 4 minutes).
Add Swiss chard and cook until wilted (about 3 minutes). Season with salt and pepper. Taste and adjust seasonings if needed.
Assemble:
Spoon 1-2 Tablespoons breadcrumbs onto crust, leaving 1 inch clearance around the circumference to fold galette.
Spread filling on top.
Gently fold edges of pie dough towards the center around all the sides. Sprinkle edges with breadcrumbs.
Bake for 30-35 minutes.
Let cool for at least 10-15 minutes before cutting.
Video
Notes
Mushroom and chard galettes taste best when eaten soon after baking. They can be refrigerated, but keep in mind the chard won't be quite as tasty when reheated. Because of the delicate veggies, I do not recommend that you freeze.Let leftovers cool completely before putting into an airtight container. Keep in the fridge for up to 3 days.Reheat leftovers in the oven for the best texture. Bake on a lined baking sheet for about 10 minutes in a 350 degree preheated oven