4 (½ inch) slices whole-wheat Italian bread, cut diagonally
4 teaspoons unsalted butter
Peel and core apple. Cut in half vertically. Place each half cut side down on work surface and cut crosswise into even 1/8-inch slices. Keep slices together in shape of apple.
Set cut apple halves on small, microwavable plate, still holding slices together. Sprinkle 1/2 teaspoon granulated sugar over each half and cover plate loosely with wax paper. Place plate in microwave, keeping paper tucked under plate, and microwave, about 45 seconds. Remove and let apple slices sit covered for 5 minutes. Uncover and cool to room temperature. Meanwhile, in small bowl, mix brown sugar and cinnamon.
Toast bread for crostini. Spread each slice of toast with 1 teaspoon butter and sprinkle one-fourth of cinnamon-sugar evenly over each. Cover bread with apples, placed diagonally. Serve immediately.