Butterflying a whole trout entails removing the ribs and backbone in order to lay the fish flat. Use a sharp, flexible knife to best navigate the tiny bones.
1. Place the cleaned fish on a work surface with its belly facing you. Using kitchen shears, remove the back and belly fins.
2. Starting at the tail, slide the knife between the flesh of the fish and the lower edge of the rib cage. Make short gentle cuts toward the backbone, separating the meat from the ribs as you go. Turn the fish over and repeat this step on the other side.
3. Pull back the filleted flesh, exposing the ribs and backbone. Using kitchen shears, cut through the base of the ribs along the backbone.
4. Lift out the backbone and rib cage, and flatten the fish, skin down, on the work surface.