Rinse beef shoulder to remove any residue, pat dry with paper towels and place on a utility platter. In a small bowl, make the rub for the beef by combining Smokey Rotisserie Seasoning and Garlic Pepper. Rub the seasonings into all surfaces of the beef, cover with a sheet of plastic wrap and set aside for at least 30 minutes and up to 2 hours at room temperature. (The seasonings will actually begin to "cure" the meat.)
Preheat oven to 425 degrees F.
In an oven proof skillet heat 1 tablespoon olive oil over high heat, add onion and garlic and cook until they begin to soften. Add beef and sear it on all sides. Cover pan (with lid or foil) and transfer to oven to finish beef, bringing to an internal temperature of 115 degrees F for medium rare (about 30 minutes). Remove from oven, transfer to a utility platter, and let rest for 10 minutes. (Make the sauce as directed below while the beef is resting.)
While the beef is in the oven, make the onion rings. Combine flour, baking powder and salt in a large bowl. In another smaller bowl, whisk together oil, milk, egg and black pepper. Add the egg mixture to the flour mixture and combine until all dry ingredients are moistened. Heat oil to 375 degrees F in a deep-fryer. Add the onion rings to the bowl of fritter batter. Using tongs, transfer batter-coated onion rings to the deep-fryer basket, deep-fry in hot oil until golden brown and drain. Keep in a warm place.
For the sauce: To the pan in which the beef was roasting (use an oven mitt on the hot handle), add 1 cup water and balsamic vinegar over medium high heat and whisk in instant flour. Allow to cook for about 5 minutes to "cook out" the flour. Strain into a bowl and whisk in gorgonzola cheese, allowing it to melt. Season with pepper, to taste, and salt only if needed (as the cheese will lend saltiness).
Slice beef into steaks, and transfer to serving dish. Spoon cheese sauce over meat and top with onion rings.