Why does the cheese at a diner melt so uniformly over a thick burger without burning the bread? The secret lies in separating the toast phase from the melt phase, treating the griddle as a multi-zone cooking station rather than a single flat surface.
Ground beef contracts significantly as rendered fat cooks out. To prevent the patty from shrinking into a thick, rounded disk that slides out of the sandwich, shape the raw meat slightly larger than your slice of rye bread and press a deep indent into the center. Fat content matters here; using an 80-20 grind ensures enough internal moisture so the beef does not dry out during the three-minute sear per side. Sauté your onions separately in butter for roughly 10 minutes until translucent and sweet, then push them to a cooler edge of the pan to maintain heat while the beef finishes.
Achieving a glossy, fluid cheese melt without overcooking the beef requires controlled moisture. Place two slices of cheese directly onto the hot patty, cover the meat with a domed lid that clears the top of the cheese, and introduce a single teaspoon of water underneath the cover. The trapped steam acts rapidly, melting the dairy solids in under 30 seconds. Meanwhile, fry the buttered rye bread separately until golden brown. Assemble by spreading Thousand Island dressing on the un-toasted interior sides, layering the onions and the steamed patty, and pressing gently before slicing diagonally.