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How to blacken fish
Heat a dry cast iron pan over medium-high heat.
A cast iron pan is a required tool for blackening fish, as other pans aren't capable of delivering the intense heat needed for this preparation. Set the pan onto a charcoal grill or a propane burner set to medium-high heat.
Allow the pan to heat for about 10 or 15 minutes, and do not add any oil to the pan. Melt some butter in a shallow pan.