Smoked Salmon Mousse and Cucumber Tea Sandwiches

INGREDIENTS

• 3 English (hothouse) cucumbers, peeled
• and thinly sliced crosswise
• 1 lb. smoked salmon, diced
• 1/4 cup mayonnaise
• 1/4 cup sour cream
• 1 Tbs. chopped fresh dill, plus sprigs for garnish
• 1 tsp. freshly ground pepper
• 3/4 cup chilled heavy cream
• 20 thin slices pumpernickel bread
• 8 Tbs. (1 stick) unsalted butter, melted