Zesty Lemon Bar Sheet Cake with Buttery Crust

Ingredients

• 3 cups crushed shortbread cookies (about 11-15oz blended into fine crumbs)
• 5 tablespoons melted unsalted butter
• 1 tiny dash salt
• 1 tablespoon grated lemon peel (roughly 1 lemon)
• 3/4 cup room temp buttermilk
• 2/3 cup room temp sour cream
• 3 whole eggs at room temp
• 1 egg white at room temp
• 1 tablespoon pure vanilla extract
• 1 teaspoon lemon extract (if you want)
• 1/3 cup veggie oil
• 1/4 cup plain flour
• 1 box (15.25oz) lemon cake mix (try Duncan Hines)
• 3 egg yolks
• 1 whole egg
• 3/4 cup white sugar
• 1/2 cup fresh lemon juice
• 2 tablespoons grated lemon rind (roughly 2 lemons)
• 4 tablespoons unsalted butter
• 1 1/2 cups barely softened unsalted butter
• 1 teaspoon lemon extract
• 1 tablespoon vanilla extract
• 1/4 cup heavy cream
• 6-7 cups confectioners sugar
• 1 drop yellow food gel coloring
• 1 cup crumbled shortbread cookies