Preheat the oven to 325 degrees F (165 degrees C).

To make the beef stew: Heat oil in a large Dutch oven over medium-high heat until very hot. Working in 2 batches, cook and stir beef in hot oil until browned. Return all of the meat to the Dutch oven, sprinkle with flour, and stir lightly to coat. Stir in beer, onion, carrot, bay leaves, Worcestershire sauce, garlic, thyme, salt, and pepper. Bring to a boil and cover.

Place the Dutch oven into the preheated oven and cook for 45 minutes. Uncover, stir, and cook until beef is very tender and liquid is reduced by half, about 45 more minutes.

Meanwhile, to make the colcannon: Cook bacon in a large, deep skillet over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain bacon on a paper towel-lined plate. Crumble bacon and set aside.

About 30 minutes before stew is ready, place potatoes into a large pot and cover with salted water. Bring to a boil, then reduce heat to medium-low, cover, and simmer until tender, about 20 minutes. Drain and allow to steam dry, 1 to 2 minutes.

Place cabbage into a microwave-safe bowl and add 1 to 2 tablespoons water. Cover and microwave on high for about 2 minutes 30 seconds; uncover (watch out for steam) and stir cabbage. Cover again and microwave until cabbage is slightly tender but not mushy, about 2 minutes 30 seconds more. Drain excess liquid and set cabbage aside, covered.

Place potatoes into a large bowl; add warm milk, butter, salt, and pepper. Beat with an electric mixer until smooth and creamy. Stir in cabbage, crumbled bacon, and parsley until well combined.

To serve, place a scoop of colcannon onto a plate, make a hollow, and fill with beef stew.