For your top crust, In a bowl, stir together your flour and salt. Using two butter knives, held against each other with one in each hand to form an “X,” cut your butter into your dough, with the knives pulling away from each other and back in, until you have a sand-like consistency
Add in your water (I like to put a few ice cubes in a glass before filling it with cold water to make sure it’s extra cold), stir together, and then compress the dough into a ball. See notes below if you have a food processor!
Place your dough ball between two large pieces of parchment paper, and roll to ⅛” thickness - making sure your dough is an even thickness throughout.
Gently peel the parchment back from the top layer, lay it back onto the dough, flip all of it over, and repeat with the bottom (now top) layer of parchment. Invert your pie dish onto the center of your rolled dough and cut a circle, leaving about an inch from the rim of your pie dish. Save the scraps for future use!
Cover your dough with the other piece of parchment paper and place your flat crust in the fridge for 15 minutes while you make your filling
Heat a large skillet on the stove over medium-high heat
Add your olive oil to the pot along with your diced carrots, onion, mushrooms, celery, salt, and ground pepper. Saute for 7-8 minutes until cooked down and the mushrooms and onions start to get some color on them
Add in your garlic and cook an additional 2 minutes, until fragrant
Stir in your herbs and cook for an additional 1-2 minutes
Add in your prosecco and use it to scrap any bits off the bottom of the pot. Cook until prosecco is absorbed into the veggie mix
Add in your 2 ½ tablespoons of flour, stirring to evenly coat your veggies, then add your butter. Combine until you have an almost paste-like mixture
Add your diced parboiled potatoes* and stir to combine
Pour in your broth, and stir to bring everything together before bringing the pot to a boil. Reduce to a simmer and simmer for 20 minutes, until the mixture has thickened. Be sure to stir occasionally, scraping any bits off the bottom
Add in your milk/cream about 15 minutes in, when it’s thickened slightly. Stir and continue cooking. When done, it should resemble a stew-like texture
Remove from the heat and stir in your peas and corn
Pour into your pie dish, spread evenly, and cool slightly for 5-10 minutes
Sprinkle 1 tsp flour over the top of your filling, this will help prevent the underside of your top crust from being soggy
Cover with your rolled-out top crust, folding in the edges and crimping, and cut a few slits from the center, to vent the pie as it bakes
In a bowl, whisk together your egg and a splash of water or milk. Brush across the top of your pie crust and sprinkle with flaky salt and sesame seeds if desired
Preheat your oven to 400F and bake for 35-40 minutes until the crust is golden brown, rotating halfway through
Allow to cool for 15 minutes before slicing and serving
Enjoy!