What is the brown stuff stuck to the pan?

When meat sears, some of its proteins and juices brown directly onto the metal. That layer — fond, French for 'base' — is concentrated Maillard flavor, the same compounds that make the crust on the meat taste good, stuck where you can't eat them. Yet.

Deglazing is the recovery: pour in a splash of liquid (stock, water, wine — almost anything), and the fond dissolves off the pan with a satisfying hiss and a scrape of the spoon. Simmer to reduce it, and you've concentrated it back into intensity. Swirl in cold butter off the heat, and the sauce turns glossy and rich.

This is why the app keeps telling you not to wash the pan yet. It's also why stainless steel is eventually worth owning: it grips fond better than nonstick, which barely makes any.

Sear, deglaze, reduce, butter. Four moves, thirty seconds each, and pan-seared-anything becomes a restaurant plate.