For the spicy mustard:
Grind the seeds in a spice grinder (or use a mortar and pestle). Combine with the rest of the ingredients, mix well and let rest at room temperature. Best if made the day before.
For the brats:
1. Place a Dutch oven over medium heat. Add butter, onions, garlic, salt and pepper. Simmer until the onions are soft and translucent. Add beer, pickle juice and red pepper. Bring to a simmer and slightly reduce. Add the brats and simmer until the brats reach an internal temperature of 150°F.
2. Meanwhile, set up the grill for medium direct heat.
3. Remove the brats and place on the grill. Turn frequently until a golden brown color is achieved and remove.
4. Turn up the heat the heat on the onions to reduce the beer until it sticks to the onions.
Toast buns then add a brat, beer onions and spicy mustard.