Preheat oven to 350 degrees Fahrenheit.
Line a 9"x13" cake pan with parchment paper so it hangs over the edges.
For the cookie bars, in the bowl of an electric mixer, cream together softened butter, granulated sugar, sour cream, lemon zest, eggs, and lemon juice until combined. Scrape down the sides in between.
In a separate bowl, whisk together flour, salt and baking soda.
Add flour mixture to wet mixture and mix just until incorporated.
Press dough evenly into the prepared parchment-lined pan.
Bake for approximately 17-19 minutes, or just until set and baked through. The bars shouldn't be jiggly, but they will be more firm to the touch. Check them often and don't over bake! Mine didn't have any browning on top. Let the bars cool completely on a cooling rack.
Prepare the frosting by creaming together softened butter, lemon zest, strawberry puree, lemon juice and powdered sugar. Frosting should be creamy and perfect as is, but if it's not, you can add a little bit of milk to thin or a little more powdered sugar to thicken. Frost cooled bars, slice and enjoy.