Prepare Crostini. Peel and devein shrimp, leaving tails intact (if desired). Rinse shrimp; pat dry with paper towels. In a large saucepan, cook shrimp in a large amount of boiling salted water for 1 to 3 minutes or until shrimp are opaque; drain. Rinse shrimp with cold water; drain again. Cover and chill until needed.
Meanwhile, in a food processor or blender, combine beans, sweet pepper, the snipped chives, and the garlic. Cover and process or blend for 1 to 2 minutes or until mixture reaches a creamy consistency. Add mascarpone cheese, salt, and white pepper. Cover and process or blend until well mixed.
Spoon about 1 rounded teaspoon of the bean mixture onto each crostini and top with a shrimp. Garnish with chive pieces. To store any remaining bean mixture, transfer to a small bowl. Cover and chill for up to 3 days. Makes 24 appetizer servings.
Cut French bread into 1/2-inch diagonal slices. Arrange bread slices on baking sheets. Lightly brush one side of bread slices with olive oil. Bake in a 400 degree F oven about 8 minutes or until lightly browned, turning once. Cool. To store, place in an airtight container and store at room temperature.