Preheat oven to 350°.
Coat an 8-inch square baking pan with cooking spray.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 3 ingredients. Set aside.
Beat sugar and butter with a mixer at medium speed until well blended. Add sour cream, vanilla, and eggs; beat well. Add flour mixture to butter mixture, beating just until dry ingredients are moist. Combine brown sugar, pecans, and cinnamon in a small bowl.
Spoon 1/2 of batter into prepared pan; sprinkle evenly with 1/2 of brown sugar mixture. Spoon remaining batter over brown sugar mixture, and spread evenly. Sprinkle remaining brown sugar mixture over batter. Bake at 350° for 40 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 15 minutes on a wire rack.
Combine powdered sugar, milk and 1/2 teaspoon vanilla in a small bowl; stir until smooth. Drizzle over coffee cake.