Pour in the beer; add butter and onions into slow cooker and turn on to high.
Heat a grill pan or heavy skillet to medium high and grill or sear the brats on all sides.
Place your Johnsonville Brats into the slow cooker and heat until the brats are cooked through, about 2 hours. Brats are fully cooked when the internal temperature reaches 160 degrees F.
Reduce heat to low to keep the brats in the slow cooker hot throughout the game.
When folks are ready for seconds or thirds -- or even when stragglers show up late --grab a Johnsonville Brat out of this indoor hot tub and enjoy!