Preheat oven to 350°F/177°C.

Line a 9x13 pan with parchment paper.

Cream the butter and sugar in a large bowl with a handheld mixer until light and fluffy, about 2 minutes. To the bowl, add the egg yolks, sourdough discard, and vanilla extract, and mix until incorporated.

In a separate bowl, combine the flour, salt, baking powder, and lemon zest.

​Add the wet ingredients to the dry ingredients and mix just until a soft dough forms.

Scoop the cookie dough into the parchment-lined pan evenly in the pan. Press dough in an even layer.

Place the pan into the preheated oven and bake for 25 minutes or until the edges are lightly golden brown.

Remove the pan from the oven and place it on a cooling rack. Allow to cool completely before decorating.

In a medium bowl, mix the cream cheese with a handheld mixer until smooth. Add the vanilla extract, heavy cream, and powdered sugar. Mix for an additional minute to whip some air into the frosting.

Tip: For a smooth cream cheese frosting, whip the cream cheese smooth before adding the liquid ingredients. Also, sift the confectioners' sugar through a mesh strainer to remove the lumps.

Wash and dry the fruit. Cut off the green tops and slice strawberries lengthwise.

Spread the cream cheese mixture evenly over the cooled crust with an offset spatula. Add the berries in a flag pattern. Add the blueberries into the top left corner of the cookie. Arrange the strawberries in 4 lines.

Refrigerate until ready to serve. Best if served immediately.

Tip: If serving on a platter, remove the cookie from the pan before adding the fruit. Loosen the cookie crust from the sides of the pan and lift, using the parchment paper as handles, onto the serving platter or large cutting board.

Cover the fruit cookie with plastic wrap and refrigerate for up to 3 days. The fruit pizza is best the day it's served. The cookie base holds up well, but over time, the fruit begins to soften and weep into the frosting. This doesn't affect the flavor, but it isn't as aesthetic.