Make the onion gravy by placing the butter and olive oil in a Dutch oven over medium heat. Add the onions and cook, stirring occasionally, for 25-30 minutes, or until golden brown.
Add the minced garlic and flour then cook, stirring constantly, for 1 minute. Slowly add the beef stock and Worcestershire sauce while stirring constantly. Reduce the heat and simmer for 10-12 minutes or until sauce thickens. Taste and season with sea salt and freshly cracked pepper, to taste.
Meanwhile, make the mashed potatoes by cooking potato chunks in a large pot of salted boiling water until fork-tender.
Warm the milk and butter in the microwave for 30 seconds.
Drain the potatoes then place them back into the pan.
Add the milk/butter to the potatoes along with sea salt and freshly cracked pepper, to taste.
Mash using a hand masher until creamy and smooth. Taste and re-season if needed. Place lid on the potatoes until ready to serve.
Cook the sausages while the potatoes are cooking and the onion gravy is simmering, by heating a grill pan over medium-high heat then coat with cooking spray.
Add the bratwurst to the pan and cook, flipping occasionally, for 10-12 minutes; making sure all sides of the bratwurst get grill marks and the sausages are cooked through.
To serve, spoon some potatoes in a bowl then top with onion gravy and a bratwurst. Sprinkle the top with freshly chopped parsley. Serve immediately. Enjoy.