Never tried cooking brats like this before, but wow, what a game-changer!

Ready your oven for baking at 350°F (175°C).
In a large Dutch oven or oven-safe pan, melt the butter and olive oil over medium heat.
Toss in the sliced onions and sauté, turning occasionally, for 20 to 25 minutes, or until tender and browned. Caramelizing onions slowly gives forth their inherent richness.
Saute the minced garlic for two or three more minutes, or until it begins to release its aroma.
Arrange the bratwursts in a nest with the onions in the pan.
Before adding the brats to the pan, make sure the liquid is almost covering them with beer and beef broth. Add Dijon mustard and pepper and salt to taste. Stir to combine.
Once the mixture reaches a simmer in the skillet, move it to the preheated oven.
If you want your bratwursts well cooked and flavored, bake them uncovered for 30 to 40 minutes.

Serve with chopped fresh parsley as a garnish if preferred.
Changes and Hints
Sliced bell peppers, in addition to the onions, provide a colorful and flavorful variation. If you’re looking for a little extra heat, try using an IPA or some red pepper flakes, or a beer with more hops. When caramelizing the onions, add a teaspoon of brown sugar for a little sweetness if you want. In case you happen to have any leftover beer brats, don’t hesitate to add them to sandwiches or slice them and serve them over pasta for another hearty dish.