What beer you use matters. Dark beers tend to be more full bodied and malty and sweet. They will work well in this stew. Hoppy beers like IPA or pale ale are too bitter for this stew and should be avoided. For this recipe we've used Moylan's Kilt Lifter, a Scottish ale, and also Ommegang Abbey Ale. A soft Belgian beer like Flanders Red or one of the Chimay beers would also be ideal.
1 Melt the butter in a large, heavy pot with a lid, such as a Dutch oven, over medium-high heat. Pat the chicken thighs dry with paper towels and set them skin side down in the butter. Salt the meat side lightly. Brown the chicken on both sides well. Remove the browned thighs from the pan and set aside in a bowl.
2 The chicken skin has likely rendered quite a bit of fat. Drain off all but 2 tablespoons of fat from the pan, taking care to not discard any of the tasty browned bits. (Note, do not discard the fat down the drain, you may clog your plumbing. Pour off into a jar.) Lower the heat to medium and add the sliced onions to the pan. If you want, sprinkle brown sugar over the onions. This is optional. The added sugar will intensify the natural sweetness of the onions. Cook the onions slowly, stirring occasionally, until they begin to brown, about 15 minutes.
3 Add the bay leaves, thyme, mustard, 2 teaspoons of salt, and beer to the onions. Scrape up any browned bits from the bottom of the pot with a wooden spoon. Add the chicken thighs and the chicken stock and bring to a simmer.
4 Cook covered for 45 minutes, then uncover the pot and simmer well until the liquid is greatly reduced and the meat wants to fall off the bone, between 45 minutes and 1 hour. If you are using unsalted or low sodium stock, you will likely need to add more salt. Add freshly ground black pepper and more salt to taste.
Serve over egg noodles or with rice or potatoes.