How to Make It
Melt 2 tablespoons of the butter in a medium skillet. Add the onion and water and cover with a piece of moistened, crumpled parchment or wax paper. Cook over low heat, stirring once or twice, until the onion softens, about 10 minutes. Add the chicken stock, cover partially and simmer for 10 minutes. Season with salt and pepper and keep the onion warm.
Using a sharp paring knife, make a lengthwise slit in a lime leaf along the vein, without cutting through either end. Carefully slip a scallop into the slit. Repeat with the remaining scallops and lime leaves. Season the scallops with salt and cayenne.
In a large skillet, melt the remaining 1 tablespoon of butter in the olive oil. Add the scallops and cook over high heat until golden on the bottom, about 2 minutes. Carefully turn the scallops and cook until opaque throughout, about 2 minutes longer.
Spoon the onion sauce in the center of warmed plates and arrange the scallops on top. Sprinkle with the nutmeg and serve.
Do not be fooled by bright white scallops at the fishmonger—that perfect color usually indicates the scallops were soaked in a preservative solution that leaks out in the pan and prevents browning. Look for scallops that are not soaking in any liquid and are less uniformly white, or even ivory, in color. To help ensure browning, dry them well between paper towels before cooking.