In a medium, oven safe sauté pan add the 2 tablespoon of butter and heat/melt slowly. After the butter foam has dissipated, add the thick sliced mushrooms and brown on both sides, seasoning to taste with kosher salt and fresh cracked black pepper. Remove the mushrooms to a plate and set aside. In the same pan add a “glug” of olive oil and and begin to heat. Stack the pancetta on top of each other, roll, and cut into thin ribbons (chiffonade). Pan fry the pancetta until crisp. Remove and set aside. In the same pan with oil and pancetta drippings, add the thinly sliced onions. Add more olive oil if needed. Season to taste with the kosher salt and black pepper. Sauté the onions until tender and caramelized. Remove from the pan. Preheat your oven to 425°. Add a few “glugs” of the olive oil to the pan, enough to coat the bottom and sides with a shallow layer. Place the oiled pan into the oven. In a large mixing bowl, crack and add the eggs along with the milk, chopped garlic, and optional red pepper flakes. Whisk thoroughly to combine. Add the leftover green bean casserole and gently mix in evenly. Add the Asiago cheese, sautéed mushrooms, pancetta, and cracked black pepper to taste then gently mix in completely. Remove the hot pan from the oven carefully and place onto the stove. Turn the heat to medium high and pour in the egg mixture. Cook the frittata a bit by pulling the side of the partially cooked batter to the center, and evenly smoothing out the solid ingredients. Repeat more than once until the frittata is 50% cooked and the bottom is just set. Place the hot pan back into the oven and bake an additional 10-15 minutes, depending on the size of your pan, until the frittata has puffed slightly in the center and fully cooked. While the frittata is baking, add the cranberry sauce and balsamic vinegar to a sauce pot. Heat and allow the jellied cranberry to melt, mix the sauce and bring to a simmer, always stirring. Cook until the sauce is syrupy and reduced making sure not to burn. Once the frittata is out of the oven, roughly cut or scoop the burrata cheese and “dot” the top of the frittata with the cheese. Next, scatter the caramelized onions on top. Cut the frittata into the appropriate pie shaped slices that you need. Drizzle the top with the cranberry-balsamic glaze and serve hot. Enjoy!