Season the beef generously with salt and pepper. Sprinkle 2 tablespoons of the flour evenly over the meat.
Heat the olive oil in a large heavy saucepan or Dutch oven over medium-high heat. Add the beef in a single layer without crowding the pan (work in 2 batches if necessary) and cook, turning, until browned on all sides. Remove the beef from the pan and reserve.
Add the beer to the pan and use a wooden spoon to scrape up any browned bits stuck to the bottom of the pan. Bring the liquid to a boil and cook until it is reduced by half; return the beef to the pot and add the potatoes, onions, carrots, celery stalk, broth and 1 cup water. Bring to a boil, reduce the heat to a very low simmer, cover and cook until the beef is very tender, 1 1/2 to 2 hours.
In a small bowl, mash the butter with the remaining 3 tablespoons flour until smooth. While whisking the liquid, drop small pieces of the butter paste into the stew, whisking until each piece dissolves. Continue adding the butter paste until it is used up and completely dissolved into the stew. Add the peas and continue cooking until the stew is thickened and the peas are cooked, about 5 minutes. Taste and season with salt and pepper (about 1 1/2 teaspoons salt and 3/4 teaspoon pepper).
Ladle the stew into individual bowls and garnish with the chopped celery leaves and sliced scallions, if using.
Adapted from "The Comfort Table" by Katie Lee. Copyright Simon Spotlight Entertainment 2008. Provided courtesy of Katie Lee. All rights reserved.