If you can plan ahead, season the beef with salt and pepper the night before you make this, covering it loosely and refrigerating it. Otherwise, try to season it at least an hour ahead and just leave it on the counter. Heat the oven to 300°F. Heat the oil in a deep, heavy ovenproof skillet or a Dutch oven over medium-high heat. Brown the beef well, until it’s crusty on all sides. Transfer the beef to a plate. Add the onions, thyme, and bay leaf to the pan, along with a big pinch of salt. Cook, stirring often, until the onions have softened and reduced in volume by about half. The onions will release some of their juices, so scrape the bottom of the pan and use these juices to release any of the browned bits from the beef. Pour in the beer and water, and crumble in the bouillon cube. You might want to grind in some more pepper at this point; I usually do. Rinse the mushrooms under hot water, chop them, and add them to the pot. (Don’t worry that you haven’t reconstituted them; you’ll be doing that directly in the sauce for the pot roast and getting all their flavor.) Bring the sauce to a boil. Nestle the beef in the sauce, cover the pan, and slide it into the oven. Roast for 1 hour. Turn the meat over, cover the pan again, and roast for another hour, until a fork goes into the beef like butter. Put the beef on a cutting board, tent it with foil, and let it rest for 10 minutes or so. Fold a couple of kitchen towels and rest one side of the pan on them so that it is tilted—any fat will gather at the bottom of the slope. Leave the sauce to sit for a few minutes, then spoon off the fat. Most of the onions should have almost melted into the sauce. If you’d like the sauce a bit thicker, put the pan over medium-high heat for a few minutes, and stir a few times. When you’ve got the consistency you want, turn off the heat. Stir the mustard into the sauce. Taste for salt and pepper. Slice the beef and arrange the slices on a platter. Nap with some of the sauce. Serve with the rest of the sauce on the side. Beverage pairing : Château Belgrave , Bordeaux, France. A rich, solid recipe like this can certainly take a massive, dense red wine. But this red Bordeaux is a lovely contrast. While it has the flavor, acid, and tannin to provide a structural foil for the melt-in-your-mouth pot roast, it also has a medium-bodied agility, an ability to refresh the mouth while catering to the food. And there’s enough earthy complexity to appeal to the mushrooms in the dish as well.