Sprinkle with the salt, pepper, garlic powder and red chili flakes. Place the sliced cold butter on top of the onions
Add the raw brats on top.
Pour over the beer.
Cook on HIGH for 4 hours (It takes this long for the onions to tenderize.)
After the cooking time is up, you'll want to grill or brown the brats. You can do this in a grill pan, a bbq or even in a regular skillet. (You may need to do this in 2 batches).
Pour off all but a inch of the liquid from the slow cooker and add the brats back in. Set the slow cooker to warm and serve on buns with the onions (and mustard too if you want).
Serve and enjoy.
Notes
Place the leftover brats in an airtight container and keep them in the fridge for up to 4 days. Reheat them over medium heat on the stovetop until hot throughout. Use a bit of leftover broth so they do not burn.
You can use the leftover broth, beer, and onions for a dish like Shepherd's Pie or turn it into a delicious gravy.
Nutritional values do not include buns or other condiments.