Preheat oven to 350°. Cut bread diagonally into 1/4-inch-thick slices (about 40 slices). Place on a baking sheet. Brush tops with butter. Bake 12 to 14 minutes or until golden brown. (Bread may be stored in an airtight container up to 3 days.)
Pick crabmeat, removing any bits of shell. Gently toss crab with sherry, parsley, hot sauce, and 1/2 tsp. salt in a bowl; cover and chill 1 to 24 hours.
Meanwhile, stir together sour cream, next 5 ingredients, and remaining 1/4 tsp. salt until blended; cover and chill 1 hour to 3 days.
Spoon rounded 1/2 tsp. sour cream mixture onto each bread slice; top each bread slice evenly with crab mixture. Garnish, if desired. Serve immediately.