Combine flour, baking soda, salt, sugar, eggs, and sour cream. Beat at medium speed of an electric mixer until blended.
Combine 1 cup butter and water, lemon rind, lemon juice and lemon extract in a medium saucepan. Bring to a boil. Add to flour mixture, stirring well. Pour into a greased and floured 15 x 10 x 1 inch jellyroll pan.
Bake at 350 degrees for 20 minutes or until a wooden pick inserted in the center comes out clean. Cool in pan on a wire rack for 20 minutes.
Combine remaining 1/4 cup plus 2 tbsp of butter, milk and 1 tsp lemon extract in saucepna; bring to a boil. Remove from heat. Gradually add powdered sugar, stirring until mixture is spreading consistency. Spread frosting on top of cake. Let cool completely in pan on a wire rack.