Stir together mayonnaise, creme fraiche, chopped dill, lemon juice, salt, and pepper in a medium bowl until well combined. Stir in shrimp.
Melt 1 tablespoon butter in a skillet over medium-high heat, and saute half the bread triangles until golden brown and crisp. Transfer to a plate, and saute remaining bread in remaining tablespoon butter.
Spoon a generous amount of shrimp mixture onto toasts. Top each toast with caviar, and garnish with dill sprigs. Serve with lemon wedges. Shrimp mixture can be refrigerated 1 day.