In a large dutch oven, heat some olive oil over medium heat. Toss the meat cubes with the 1 ½ tbsp of flour, and then in batches, brown them until seared. Remove to plate as you go.
Add more oil if you need to, then add the celery, onion, and garlic. Cook and stir until the vegetables are soft. Add the thyme and season with salt and pepper. Stir in the mushrooms, bay leaves, broth, tomato paste, and Guinness; bring to a boil, then cover and put into the oven.
Let the stew bubble away in the oven for two hours. Mean while, make the dumplings.
In a bowl, stir together flour, baking powder, a pinch of nutmeg, salt, and pepper. Cut in your bits of butter with a pastry cutter, and then stir in the cheese. Add milk, stirring until you get a wet dough. You may need more or less, use your judgment.
Spoon out portions of the dough about the size of a ping pong ball, roll them with your hands, and place on a cookie sheet. Put them in the fridge to chill while the stew cooks.
When the stew is finished, plop the dumplings in one at a time, pushing them under the juices, and then put a lid back on and allow them to cook for another 30 minutes.