Decide whether your recipe needs a paste (creamy sauce texture) or powder/purée (more flexible, often added while simmering).
Choose the closest substitute to your goal: match color first (yellow/orange), then match heat level (medium vs mild).
Start with the listed ratio, then taste: add a little salt/acid or sugar only if your dish tastes flat compared to ají amarillo.
If the substitute is drier (powder/flakes), mix it into a spoon of warm oil or broth before adding to prevent gritty texture.
If the substitute is brighter but hotter than ají amarillo, dilute with yogurt/cream, broth, or cooked purée until balanced.