Heat a skillet or grill pan over medium heat
Add bratwursts and brown them on all sides
Remove the brats from the pan
Add sliced onions to the pan
Pour in enough beer to cover the bottom of the pan
Return the brats to the pan
Bring the beer to a gentle simmer
Cover and cook until the brats are cooked through
Remove the brats from the beer
Finish the brats on a grill or in a hot skillet until browned
Serve in buns with the cooked onions and desired toppings