If you haven't already cooked your bacon, start with that. You can cook it in your cast iron or in the oven or microwave. Reserve the bacon grease in a tempered glass jar. (Warning: Be extra careful working with the bacon grease, it's hot and will burn!) Once the bacon is done cooking, break it into small pieces or dice it. Set this aside near your cooking area.
Preheat your cast iron skillet on the stove at medium-low while you chop up your vegetables. If you're cooking your bacon, you can use the waiting time to chop vegetables. I like to leave my mushrooms in pretty large pieces. You can see in the photo that the mushrooms reduce to about ⅓ of their original size once they are finished cooking.
Preheat your oven to 350 degrees.
We will begin by cooking the mushrooms. Add 2 Tablespoons of reserved bacon grease into your cast iron skillet and heat the oil on medium heat. Add your mushrooms and saute. This will take 15-20 minutes. Stir occasionally.
Prepare the frittata egg mixture by grabbing a medium sized bowl and cracking 10 eggs into it. Then add the 1 cup of half and half or cream, dried mustard, sherry, Worcestershire sauce and cayenne. Stir with a large fork or whisk until well combined. Set aside near your cooking area.
Shred ½ lb of cheddar cheese and set this aside near your cooking area. Note that when we add the cheese, we'll add ⅔ of this to the pan and reserve ⅓ to top the frittata with.
The mushrooms should be almost done cooking. Add the asparagus and onion and another ½ Tablespoon of Bacon grease and sauté until the asparagus is done when you test a bite.
Now we need to work quickly. Spread out the vegetable mixture so it's even all around and toss in the bacon pieces. Then add ⅔ of the cheese mixture and quickly toss.
Pour in the egg mixture–working to make it even as you pour it in. You may need to use your spatulato push down some of the veggie pieces.
Finally, top with the remaining ⅓ of cheese. Carefully, using hot pads, put your cast iron skillet in your preheated 350 degree oven and cook for 20-30 minutes until browned and cooked through.
Notes
The Macro Percentages on this recipe are: 70% Fat 5% Net Carbs (Total Carbs - Fiber) 21% ProteinNutrition facts & Macros are estimates only and will vary based on the unique ingredients you use and any variations you make.