Bring a large pot filled with about 4 quarts of water to a boil. Add the salt, then cook the pasta according to the package directions until al dente. Drain well and set aside.

Place a large, deep sauté pan over medium heat and warm the oil. Add the bratwurst meat, breaking it into small pieces as it cooks. Continue cooking for about 4 minutes, or until the sausage is fully browned and no pink remains.

Lower the heat to moderately low and stir in the diced onion. Cook for about 4 minutes, until the onion softens and turns translucent, scraping up any browned bits from the bottom of the pan as it cooks.

Add the minced garlic and the pinch of crushed red pepper flakes. Stir constantly for about 1 minute, just until the garlic becomes aromatic.

Pour in the beer and deglaze the pan thoroughly, loosening any remaining browned bits. Let the mixture simmer for about 3 minutes, or until the liquid has reduced by roughly half.

Add the butter and season with black pepper to taste. Stir until the butter has melted, then reduce the heat to low.

Transfer the cooked pasta to the pan and add the grated Parmesan. Toss gently just until the pasta is evenly coated and everything is well combined. Turn off the heat immediately after mixing.

Serve the pasta at once on a platter or in individual bowls. Finish with chopped parsley and extra Parmesan, if desired.