Heat oven to 350°F (325°F for dark or nonstick pan). Spray bottom and sides of 9- or 8-inch square pan with baking spray with flour.
In large bowl, beat cake mix, sour cream, oil, water and egg with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Spread in pan. Place raspberries on top of batter.
In small bowl, stir topping ingredients with fork until well mixed. Sprinkle evenly over batter and raspberries.
Bake 9-inch pan 30 to 40 minutes, 8-inch pan 35 to 45 minutes or until toothpick inserted in center comes out clean. Cool at least 30 minutes before serving. Garnish with fresh raspberries and mint leaves.