Preheat the oven to 325 degrees.
Make the beef stew by cooking the bacon pieces in a large cast iron skillet over medium heat until cooked through and the fat has rendered down. Remove the bacon with a slotted spoon and place on a paper towel.
Remove all but 1 tablespoon of bacon grease from the cast iron skillet; set the remaining bacon grease aside until needed. Return the cast iron skillet to the stove and turn it up to medium-high. Pat the beef chunks dry then season well with sea salt and freshly cracked pepper, to taste.
Add half of the meat to the HOT cast iron skillet and cook, until browned all over, about 3 minutes. Remove the beef from the cast iron skillet to a plate. Add the remaining beef to the cast iron skillet and cook the beef until browned all over, about 3 minutes. Remove to the plate and cover loosely with a tin foil tent; set aside.
Add the remaining 1 tablespoon of bacon grease to cast iron skillet over medium heat. Add the onion and cook, stirring often, until softened, about 3 minutes.
Add the minced garlic and cook, stirring constantly, for 30 seconds. Add the tomato paste and cook, stirring constantly, for 45 seconds.
Add the flour and cook, stirring it into the onion mixture constantly, for 2 minutes. Add the red wine and whisk until the mixture is well combined and reduced a bit, about 2 minutes.
Add the beef broth along with the plate of cooked beef chunks and their juices and the carrot, celery, bacon crumbles, thyme sprigs, and bay leaves. Stir then cover with a tight fitting lid and place into the oven to cook for 2 hours and 25 minutes.
Remove the lid after 2 hours & 25 minutes and continue to cook for 20 minutes to allow the beef to finish cooking and the sauce to thicken slightly.
Meanwhile make the creamy mashed potatoes by placing the potatoes, along with a sprinkling of salt, into a large saucepan and add enough water to cover the potatoes by 1 inch. Bring the water to a boil over high heat then reduce the heat to medium low and simmer until the potatoes are fork tender, about 15-18 minutes. Drain the potatoes.
Place the butter into the milk and heat in the microwave for 30 seconds; season with some sea salt and freshly cracked pepper, to taste. Pour the milk mixture onto the potatoes. Mash the potatoes using a hand masher or hand mixer until creamy and smooth. Taste and season with more sea salt and freshly cracked pepper, if needed.
Remove the beef stew from the oven and immediately turn the oven up to 375 degrees.
Skim off any fat from the surface of the stew. Remove the thyme sprigs and bay leaves. Taste and season with sea salt and freshly cracked pepper, to taste. Add the fresh peas and stir to combine.
Starting at the outer edge of the skillet, carefully spread the mashed potatoes over the top of the beef stew until evenly coated. Make a pattern with a fork to give it texture.
Place the skillet on a baking sheet in case it bubbles over while cooking. Bake for 20 minutes, or until the potatoes are starting to turn golden.
Remove from the oven and sprinkle with parsley. Serve and enjoy!