Preheat oven to 450 degrees F.
Make topping: In a small bowl stir together topping ingredients until combined well, and season with salt and pepper.
Scrub reserved clamshells inside and out and dry. In a shallow baking pan spread coarse salt about 1/4-inch deep and nestle shells in salt to keep them level. Return shucked clams to shells and cover generously with topping. Clams may be prepared up to this point 1 hour ahead and chilled.
Bake clams in middle of oven 10 minutes. Serve clams nestled in coarse salt on a platter.