Preheat the oven to 350° F and spray a 9x13 casserole dish with cooking spray.
In a medium bowl combine cake mix (dry mix only), eggs, and melted butter until well combined. The batter will be stiff.
Press cookie bar batter into the bottom of the casserole dish evenly so that bars are uniform in size and thickness.
Bake for about 20 minutes or until the top is light golden brown and the bars are set.
When bars are finished baking, allow to cool at room temperature and then refrigerate for 3 hours.
While bars are chilling whip cream cheese and butter until fluffy using a stand mixer with whisk attachment or a large mixing bowl with hand mixer.
Add lemon extract and mix until combined.
Add confectioners sugar one cup at a time and mix between each addition, scraping down the bowl between each cup.
Spread frosting evenly on cookie bars, being careful not to disturb the crumbly surface of the top of the bars.
Refrigerate bars again for at least 3 hours before cutting and serving. The longer the bars chill the easier they will be to cut smoothly. But they are also melt in your mouth delicious at room temperature, so it is just a matter of preference.
These bars will keep in the refrigerator for up to a week in an airtight container.
Notes
The calories shown are based on the bars being cut into 15 pieces, with 1 serving being 1 frosted bar. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**