3 ounces black caviar (<a href="http://russanddaughters.com" target="_blank">russanddaughters.com</a>)
Place quail eggs in a medium saucepan, and cover with several inches cold water. Cover, and bring to a boil over high heat. Turn off heat, and let sit 2 minutes, stirring several times to ensure even cooking. Transfer eggs to a bowl of ice water, and let cool completely, about 5 minutes. Remove eggs, 1 at a time, and pat dry with paper towels. Peel eggs, and halve lengthwise. Remove yolks, and reserve whites.
Mash yolks with mayonnaise, and season with salt and pepper. Stir in lemon juice.
Fill each egg-white half with 1/4 teaspoon caviar. Place a dab of egg-yolk mixture on each crostini, and place an egg half on top. Serve immediately.