Pat the beef dry and season with salt and pepper. Heat oil in a heavy, ovenproof casserole over medium-high heat.
Brown the beef in batches (3-4 minutes per side) until caramelized. Remove and set aside.
Reduce heat to medium. Add the onions to the pot and cook for 8-10 minutes until soft and beginning to brown. Stir in the garlic and cook for 30 seconds.
Pour in the ale (if using) to deglaze, scraping browned bits from the bottom. Let it reduce for 1-2 minutes.
Add the beef stock and Worcestershire sauce, return the beef to the pot. Stir in thyme, bay leaves, and adjust seasoning.
Braising
Bring to a gentle simmer, cover, and transfer to the oven. Braise for 1.5-2 hours, or until beef is tender.
Remove the pot from the oven and discard bay leaves.
Topping and Baking
Arrange the thin potato slices in overlapping layers over the beef in a circular pattern. Brush the potato top with melted butter and season with salt and pepper.
Return uncovered to the oven and bake another 30-45 minutes, until potatoes are tender and golden.
Let rest for 10-15 minutes before serving so the juices settle.
Notes
For gluten-free, skip the ale. Can be made ahead and reheated.