While the dough rests, make the filling using this matar mushroom matar recipe. Follow all the steps as it is except keep the mushrooms and peas a little undercooked/ do not dry out completely. Completely cool the filling.
Preheat oven to 400F. On a floured surface, roll the dough into a 14 inch circle about ¼ inch thick. Carefully transfer to a parchment lined baking sheet.
Place the mushroom matar filling in the centre of the rolled crust and spread it evenly leaving 1.5 inches edge. Fold the border up and over the filling, pleating if you wish. Brush with melted butter.
Bake the galette for 45 to 50 minutes. You might see bit of water from the mushrooms after about 25-30 minutes which is natural but it will bake off. If you feel that the crust is getting too brown, tent it with a piece of aluminum foil.
Once baked,sprinkle the parmesan cheese(if using) and let the galette cool on the sheet for 5 minutes and then carefully transfer on wire rack to completely cool down .Slice with a sharp knife and serve.
Storing the Leftovers - Simply place the leftover slices on a tray or plate and cover with cling film and store refrigerated for 1-2 days. Warm up slightly in a toaster oven for 3-4 minutes and serve.