Recipes: Beer brat sliders with mustard

Preparation:   Preparation time: 35 mins Cooking time: 1 hr 10 mins Serving: 6 Ingredients: 1 large sweet onion (about 11 ounces), thinly sliced 3 fresh thyme sprigs 1 (12-ounce) bottle pale lager beer, such as Moosehead 2 tablespoons coarse-grained mustard, plus more for serving 2 tablespoons apple cider vinegar...