Make the cookie cake:

1. Preheat oven to 350°F (180°C). Prepare a 9-inch cake pan with parchment paper in the bottom and baking spray on the sides. Set aside.
2. Combine the flour, baking soda and salt in a medium sized bowl and set aside.
3. Cream the butter and sugar together in a large mixer bowl on medium speed until light in color and fluffy, about 2-3 minutes. Scrape down the sides of the bowl a few times to be sure all is well incorporated. You should be able to see the change in color and texture happen and know it’s ready.
4. Add the egg and vanilla extract and mix until well combined.
5. Add the lemon juice and lemon zest and mix until well combined. Cookie dough may look a little curdled.
6. Add the dry pudding mix and other dry ingredients and mix until the dough is just combined. Do not over mix.
7. Stir in the white chocolate chips.
8. Press the cookie dough evenly into the cake pan. Press a few more white chocolate chips into the top of the cookie cake, if desired.
9. Bake for 19-24 minutes, or until the edges just begin to turn golden.
10. Remove from oven and allow to cool completely in the cake pan, then transfer to a serving plate. It it’s fully cool, you should be able to flip it upside down onto a cooling rack, place another cooling rack on top (which is actually the bottom) and then flip it back over so that it’s right side up.

Make the frosting:

1. To make the frosting, beat the cream cheese and butter until smooth.
2. Slowly add 1 cup of powdered sugar. Mix until combined.
3. Mix in the vanilla extract and lemon zest.
4. Add the rest of the powdered sugar and mix until smooth.
5. Pipe the frosting onto the edges of the cookie cake, then store in an airtight container until ready to serve. Because of the cream cheese frosting, it should be refrigerated, but should be served at room temperature. Best if eaten within 4-5 days.