In a 10-inch cast iron skillet placed over medium high heat, add olive oil and chicken sausage. Crumble chicken sausage and cook until it is done. Remove the chicken sausage crumbles from the pan and set aside. Drain off excess grease from the pan.

In a large bowl, beat the eggs, milk, and seasonings well. Then add the grated jack and Gruyère cheese. Set the bowl aside.

Add 1 tablespoon butter and a drizzle of olive oil to the pan and add mushrooms and onions, cooking it over medium heat for 1 minute. Add baby kale, stir and cook for 2 minutes. Add diced serrano pepper and crushed roasted garlic, cook for 1 additional minute.

Add remaining butter to the pan and then add butternut squash and chicken sausage crumbles. Cook for 1 minute, and then add the beaten egg mixture to the skillet over the vegetable and chicken sausage mixture. Cook the frittata over medium heat for 8-10 minutes. Gently loosen the egg mixture from the side of the pan using a spatula during the first few minutes of cooking, so the frittata will not stick to the sides of the pan.

Sprinkle the grated Parmesan cheese on top before placing the pan in the oven to broil for 1-2 minutes. Do not let the top overbrown.

Remove the pan from the oven and let it cool for at least 3-5 minutes before slicing to serve.