Karahi is possibly the most ordered dish in any Pakistani restaurant from Lahore to London. It is deceptively simple — chicken, tomatoes, ginger, chillies, a few whole spices — but the technique separates a transcendent karahi from a mediocre one. The secret is heat and patience. High heat forces the tomatoes to release their water rapidly, and then patience allows that water to fully evaporate and the tomato solids to fry in the oil until they form a dense, caramelised masala. That process — called bhunnai — is where all the flavour lives.
Traditionally, karahi is cooked in a thick iron karahi (wok) over a wood or gas fire hot enough to generate a visible char on the bottom of the pan. At home, your biggest, heaviest pan on the highest flame is the closest substitute. Do not use a non-stick pan for this recipe.