Preheat the oven to 350°F (180°C).
Bring a large pot of water to boil over high heat and add the potatoes. Cook in gently boiling water for 10-15 minutes, until they are tender and can easily be pierced with a fork.
Drain the potatoes in a colander.
Divide the potatoes into two medium bowls and mash half of them. Set aside.
Heat 2 tablespoons of olive oil in a large skillet over medium heat.
Add the onion and garlic, and sauté until the onion is translucent, about 2 minutes.
Add the carrots, celery, corn, peas, chickpeas, parsley, thyme, and rosemary. Add salt and pepper to taste, and stir.
Stir and cook over medium heat for about 15 minutes, until the vegetables are tender but still slightly firm.
Sprinkle the flour over the vegetables and mix well.
Pour in half of the vegetable broth and stir.
Pour in half of the remaining vegetable broth and cook for about 2 minutes while continuing to stir.
Add in the white miso paste and stir well.
Pour in half of the remaining vegetable stock and cook for about 2 minutes while continuing to stir.
Incorporate the mashed potatoes and enough of the remaining stock to reach your desired consistency.
Add the diced potatoes and stir.
Pour the vegetable mixture into a 9-inch (23-cm) baking dish.
Use remaining olive oil on the outside rim of the baking dish, so the edges of the pie crust do not stick.
Top with the refrigerated pie crust, pressing the crust against the outside edges.
Beat the egg and lightly brush over top of the pie crust.
Make a small X-shaped incision on the top of the crust.
Bake for about 45 minutes or until the pie crust is golden.