Divide the beef into two equal balls and flatten lightly into patties. Season with salt and pepper.

Heat a skillet over medium-high and sauté the patties until browned and cooked through, about 3–4 minutes per side for medium.

Cook the bacon until crisp and set aside on paper towels. Sauté the sliced onion in the beef pan for 4–5 minutes until soft and golden.

Whisk together eggs, heavy cream, milk, garlic powder, salt, and pepper until smooth and slightly frothy.

Dip each bread slice into the egg mixture, letting it soak briefly but not fall apart. Cook in a buttered skillet over medium heat until golden and slightly crisp on both sides, about 2–3 minutes per side.

Spread Big Mac sauce inside if using, place a beef patty on two slices, top each with a slice of cheese, two bacon strips, and the cooked onions.

Finish with a piece of French toast on top and press gently. Serve hot.