Brush 4 large squares of foil with melted butter. Put a salmon steak on each square,
season, and top with a tarragon sprig and a slice of lime. Wrap the foil around
the salmon. Put on a baking sheet, and bake in a 300°F (l50°C) oven for 25 minutes
or until the fish is opaque and the flesh flakes easily.
Meanwhile, make the avocado sauce: put the flesh of 1 avocado into a food processor
with the yogurt, lime zest andjuice, and salt and pepper to taste and puree until
smooth." Transfer to a serving bowl. Dice the remaining avocado and stir into the
sauce.
Unwrap the salmon, transfer to warmed serving plates, and serve immediately with
the avocado sauce.