salt a large pot of water, and bring to a boil. put in potatoes and cook until tender. drain water, add 4 tbsps of butter, mix and mash. add sour cream and scallions and mix completely until creamy.

in a large skillet melt 2 tablespoons of butter on medium heat. add shallots and simmer for 10 minutes, stirring often. add garlic, and cook, continuing to stir for 3 minutes. add in all of the mushrooms, poultry seasoning, stir well and cook for 15 minutes. add in frozen corn and peas, salt and pepper, mix well and let cook for 3 minutes. cover and remove from heat.

in a large casserole baking dish, put the mushroom mixture in the bottom, filling the dish halfway. layer on top, the mashed potatoes. brush the egg on top of the potatoes. use fork and lightly press the tines into the potatoes, all over for texture.

bake at 375 degrees for 45 minutes, or until top starts to get golden brown.