Prep: Prepare your pie crust according to recipe or package instructions. Grease or line a 9” pie pan and par-bake the bottom crust. Keep the top crust chilled until just before baking in step 6. Preheat the oven to 425F.
Make the Sauce: Whisk the flour, nutritional yeast, salt, and milk together in a small saucepan over medium-high heat. Bring the mixture to a simmer, then reduce the heat to medium and simmer for 3 minutes, whisking constantly, until the sauce has thickened. Set aside; the sauce will thicken further.
Aromatics: Melt the butter in a large sauté pan with a lid over medium heat. Add the onion, celery, and carrot and sauté for 3 minutes, until the onion is translucent. Add the thyme, smoked paprika, and black pepper; sauté for an additional 2 minutes, to toast the spices.
Cook the Potatoes: Add the potatoes to the pan and mix well, then add 1/4 cup (60 ml) water to the pan and cover. Cook for 5 minutes, to steam the potatoes.
Make it Saucy: Uncover the pan and add the chickpeas and peas. Mix well, then turn off the heat. Add in the prepared sauce and mix until evenly distributed to complete the pie filling.
Assemble: Roll out the top pie crust according to recipe instructions. Transfer the chickpea filling to the par-baked crust, then top with the remaining crust. Use a fork to crimp the two pie edges together, then use a knife to cut a “X” in the center of the pie dough to allow for ventilation. Lightly tent the pie crust in foil.
Bake: Bake in the middle rack of the oven for 15 minutes. Check on the pie; if if the crust is already golden, loosely tent with foil to prevent burning. Bake for an additional 10-12 minutes, checking for doneness every 5 minutes or so, until the crust is golden brown.
Serve: Let the pie sit for 5 minutes, then slice and serve warm. Store any leftovers in the refrigerator for up to 5 days.