Heat oven to 350°F. Grease and flour the bottom and sides of 9 or 10-inch springform pan. In a large bowl, combine 2/3 cup sugar and butter; beat until light and fluffy.
Add lemon peel and egg; beat 2 minutes on medium speed.
Lightly spoon flour into a measuring cup; level off. In a medium bowl, combine 1 1/2 cups flour, poppy seeds, baking soda, and salt; mix well.
Add to butter mixture alternately with sour cream, beating until well combined.
Spread batter over bottom and 1-inch up sides of greased and floured pan, making sure batter on sides is ¼-inch thick.
In another medium bowl, combine all filling ingredients; mix well. Spoon over batter.
Bake at 350°F for 45 to 55 minutes or until the crust is golden brown.
Cool for 10 minutes; remove sides of the pan.
In a small bowl, blend powdered sugar and enough milk for desired drizzling consistency. Drizzle over warm cake. Serve warm or cool.