Sliced Radishes and Watercress on Buttered Ficelle

Name: Sliced Radishes and Watercress on Buttered Ficelle
Yield: Makes 18 Servings
Ingredients: 1/4 cup unsalted butter, room temperature; 18 thin diagonal slices ficelle or other narrow baguette; Fleur de sel (fine French sea salt); 1 small bunch watercress, trimmed; 4 watermelon radishes or other large radishes, very thinly sliced; Edible flowers or daikon radish sprouts* (optional)