Slice onions and add to pan. Cook in 4 tablespoons butter. I used salted butter from Land O' Lakes. Cook until onions are almost soft.
Add beer, brown sugar, vinegar, thyme, Worcestershire sauce and stir until onoins are soft.
Add bratwurst and cook for approximately 10 minutes.
Transfer bratwurst to another pan and cook in olive oil until sides are crispy.
Return bratwurst to pan with onion/beer mixture, add cornstarch, and cook on medium heat while you cook the peppers.
Cut green and red peppers into slices. Add to a seperate pan with olive oil, salt, pepper, and garlic powder. Cook until soft.
While peppers are cooking, use the pan that you sauted' the bratwurst in and toast your bread or buns. Add butter to the pan but keep watching to make sure the buns do not burn.
When peppers are done, buns are toasted, turn the heat off and assembly your sandwich.