In a large saucepot, heat 4 tablespoons butter until shimmering. Toss the beef with the flour and add to the pan, and cook until everything has browned. The flour will start to turn into a thick paste from the meat juices.
Add the onion and potatoes and cook until the onions have started to soften, about two minutes, stirring often to make sure none of the meat sticks to the bottom of the pot. At this stage there should be plenty of liquid at the bottom of the pot, from the vegetables and juices from the meat.
Add the wine and deglaze the pan, scraping up all the browned bits from the bottom. Add the mushrooms, tomato paste and rosemary and cook together until fragrant, about two or three minutes. Add the garlic and cook one more minute or so, stirring often.
Add the water or stock and stir to combine. Turn the heat down to low and simmer for at least 1 hour (preferably 2), stirring often, until the stew has reduced by about one cup.
Serve topped with cheddar biscuits.