Heat oil in a large Dutch Oven or heavy-bottomed pot over medium-high heat. Season beef on all sides liberally with salt and pepper then place inside Dutch Oven and sear for 3-4 minutes on the top and bottom, until a golden brown crust has formed. Add carrots, celery, and shallots then cook until vegetables are tender, 6-8 minutes. Sprinkle in flour then stir and cook for 1 more minute.

Pour in wine, beef broth, and water then bring to a boil. Place a lid on top of the Dutch Oven then turn heat down to medium-low and simmer for 2 - 2-1/2 hours, or until beef can be easily shredded, turning beef over halfway through. Remove meat then shred. If liquid is not thickened, turn heat up and simmer until thickened then return beef to the pot and add peas. Transfer mixture to an oven-safe, 2-1/2 quart casserole dish set atop a baking sheet then preheat oven to 400 degrees.

About 30 minutes before the beef is done, add potatoes to a large pot of cold water then bring to a boil and cook until fork-tender. Drain then mash with butter milk, salt and pepper. Spread on top of meat mixture then bake for 10-12 minutes, or until light golden brown on top.