材料: butter (奶油) 1 stick (8 tablespoons) sugar (糖) 1 cup large egg (大蛋) 3 sour cream (酸奶油) 1 cup (8 oz) vanilla extract (香草精) 1 teaspoon cake flour (低筋面粉) 2 cups baking powder (泡打粉) 1 1/2 teaspoons baking soda (苏打粉) 1/2 teaspoon salt (盐) 1/2 teaspoon For the streusel: light brown sugar (黄糖) 1/4 cup all-purpose flour (中筋面粉) 1/2 cup ground cinnamon (肉桂粉) 1 1/2 teaspoons salt (盐) 1/4 teaspoons butter 3 tablespoons, 切成小块 chopped walnut (核桃碎) 3/4 cup