Preheat oven to 350°F. Spray 8 in. baking pan with vegetable pan spray.
In small bowl, combine flour, baking soda, baking powder and salt; set aside. In large bowl, beat butter and granulated sugar with electric mixer until light and fluffy. Add egg, egg yolk and extract. Beat well. Add flour mixture in two additions alternately with sour cream, mixing only until incorporated.
For streusel, combine brown sugar, cinnamon, flour and softened butter in small bowl; mix until crumbly. Spread half of the batter over bottom of prepared pan. Sprinkle with half of the streusel mixture. Repeat.
Bake 30-32 minutes or until cake tester inserted in center comes out clean. Cool completely. In small bowl, combine confectioners' sugar and milk; drizzle over top of coffeecake.
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