Sauté onion in olive oil in a small saucepan over medium heat. Add garlic, bay leaves, and peppercorns; sauté 30 seconds. Add vinegar and next 3 ingredients. Bring to a boil; reduce heat, and simmer, uncovered, 20 minutes or until reduced to 1 1/3 cups. Add 1/4 teaspoon sea salt and 1/4 teaspoon cracked pepper; strain sauce through a fine mesh sieve into a bowl. Keep warm.
Melt butter in a large nonstick skillet over medium-high heat. Add diced mushroom, and sauté until browned and tender; remove from pan, and keep warm.
Sprinkle scallops with remaining 1/4 teaspoon sea salt and 1/2 teaspoon cracked pepper. Heat canola oil over medium-high heat until hot. Add scallops, and cook 6 to 8 minutes, turning once. Remove pan from heat; transfer scallops to a platter. Ladle 1/2 cup sauce into pan, scraping to loosen browned bits; return to bowl. Divide sauce among serving plates; top with scallops and sautéed mushroom. Garnish, if desired.
Bistro Luneta, San Mateo, California