Heat extra virgin olive oil in a large skillet over medium-high heat. Add onions then saute until evenly caramelized, 10 minutes. Add beer, worcestershire sauce, and a little salt then bring to a boil. Turn heat down to medium then simmer until onions are tender and beer has nearly been absorbed, 10-15 minutes. Taste then add salt if necessary and set aside.
While the onions are simmering, preheat grill on high heat for at least 10 minutes (I like to let my grill get to 400-450 degrees.) Combine pork and spices - sage through nutmeg - then form mixture into 4 patties - patties will be soft, but that's ok. Turn grill down to medium heat then spray tops of patties with nonstick spray. Place patties sprayed-side down on the grill then cook for 4-5 minutes per side, or until cooked through. Briefly grill buns to soften and toast then place brat burgers onto buns and top with beer-braised caramelized onions before serving.
Notes
The fat content in ground pork can vary wildly, so don't be surprised if your burgers shrink up a bit.