Grease and flour 24 (3-inch)madeline molds. Beat sugar and yolks in a medium mixing bowl with an electtric mixer on medium to high speed for 30 seconds. Add butter, espresso powder, and vanilla. Beat on low speed until combined. Beat in egg whites until combined.
Preheat oven to 375 degrees F. Stir together flour, baking powder, baking soda, and salt in a small bowl. Sift flour mixture over the egg yolk mixture; gently fold. Fold in almonds. Spoon batter into prepared molds, filling each about half full.
Bake for 10-12 minutes or until edges are golden and tops spring back when lightly touched. Cool in molds for 1 minute. Using the point of a knife, losen cookies from molds, invert pan lightly onto a wire rack. Remove molds and cool cookies completly on rack. Drizzle with espresso icing (below) if desired. Cool completely and store at room temperature up to 3 days.
Espresso icing: Combine 1/2 tsp. instant espresso powder and 1 tbsp. water in a small bowl. Stir in 1 cup powdered sugar. Stir in additional water, 1 tsp. at a time, until it reaches drizzling consistency.