In a bowl of food processor combine beet, mustard, sour cream and olive oil. Process until creamy and smooth.
Spread butter on bread.
Fill the pastry bag with beet mousse and using Wilton tip 1M (or any similar tip), pipe the mousse into small mounds on the bread.
Place 2-3 1-inch slices of herring on each bread followed by slices of ½ an egg.
Top each bread with slices of ¼ shallot, 1 sprig of halved scallion, 1 sprig of halved green onion, 1 sprig of dill and 4 slices of cucumber.
Finish off by topping each bread with 2 teaspoons of capers.