tablespoons chopped parsley, plus more for garnish
Preheat oven to 400 degrees F. Grease a 10-inch square casserole dish.
Heat oil in a large skillet over medium heat. Cook the sausages, turning occasionally, for 8-12 minutes. Transfer to a cutting board, slice into 1/2- inch rounds and place in a large mixing bowl.
Return the pan to medium heat and add the onion, celery and garlic. Cook until softened, about 5 to 7 minutes. Season with black pepper and then add the beer. Cook for about 2 minutes then remove from heat and transfer to the mixing bowl with the bratwurst.
Add the diced pretzels, 1/2 cup cheddar cheese, thyme, stock, mustard, Worcestershire sauce, and eggs to the bowl with the bratwurst and sauteed vegetables. Stir to combine.
Transfer to casserole dish and sprinkle with remaining cheese. Bake until golden brown, about 35 to 40 minutes. Let rest 10 minutes and garnish with chopped parsley.