1. Heat oven to 350 degrees F. Line a 9 x 9 x 2-inch-square baking pan with aluminum foil, with foil overhanging pan on two sides. Coat the aluminum foil with nonstick vegetable-oil cooking spray.Make Crumb Topping:
2. Combine flour and light-brown sugar in a small bowl. Cut cold butter into 1-inch pieces and add to bowl. With pastry blender or fingertips, mix butter into flour and sugar until mixture is the texture of coarse meal. Stir in walnuts, cinnamon and cardamom until combined.Make Coffeecake:
3. Stir together the flour, baking powder, baking soda, salt and cardamom in a medium-size bowl.
4. Using an electric mixer, beat together the room-temperature butter and granulated sugar in a large bowl at medium speed until the mixture is smooth and creamy, for about 2 minutes. Add the egg and vanilla, beating until smooth. On low speed, alternately beat in the dry ingredients and milk, beginning and ending with the addition of the dry ingredients. Mix just until all ingredients are blended.
5. Spread batter evenly in the prepared pan. Sprinkle blueberries over batter in an even layer. Sprinkle Crumb Topping evenly over the blueberries.
6. Bake in 350 degrees F oven for 50 to 55 minutes or until wooden pick inserted in center comes out with no cake crumbs adhering to it. Transfer the pan to a wire rack to cool coffeecake slightly. Carefully grasp foil edges to lift from pan with coffeecake. Cut cake into squares; remove from foil. Serve warm.