Preheat oven to 350 degrees F. In a mixing bowl stir together butter, brown sugar, and the 1-1/4 cups flour until smooth. If necessary, gently knead to blend. Coat a 13x9x2-inch baking pan with nonstick cooking spray; pat flour mixture into the bottom of pan. Bake for 15 minutes or until just set.
Meanwhile, beat together eggs, granulated sugar, and 2 teaspoons of the vanilla. Stir in coconut, the 3/4 cup malted milk powder, the 1/4 cup flour, 1-1/2 teaspoons of the espresso powder or coffee crystals, baking powder, and salt. Carefully spread mixture on top of baked layer. Bake 20 to 25 minutes more or until set. Cool on a wire rack.
In a medium bowl beat together powdered sugar, the 3 tablespoons malted milk powder, the remaining 2 teaspoons vanilla, the remaining 1/2 teaspoon espresso powder or coffee crystals, and boiling water. If necessary, beat in a little additional boiling water until icing is of spreading consistency. Spread over cooled bars. Makes 36 bars.