1. Heat oven to 350 degrees . Coat an 8 x 8 x 2-inch baking pan with nonstick cooking spray.
2. In a large bowl, whisk together flour, sugar, baking powder and salt. In a small bowl, whisk together egg, milk, oil and vanilla.
3. Make a well in center of flour mixture. Add egg mixture to well and beat with a wooden spoon 1 minute, until evenly moistened; stir in chocolate chunks. Spoon into prepared pan and top with raspberries.Topping
4. In a small bowl, combine flour and sugar. Cut in butter with pastry blender until crumbly. Stir in walnuts. Sprinkle topping over raspberries.
5. Bake at 350 degrees for 35 to 40 minutes or until wooden pick inserted in center comes out clean. Cool in pan on a wire rack. Cut into 9 squares. This cake is best eaten on the day its made.