Oven and Pan Preparation: Position the oven rack in the middle and preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Grease a 9×13-inch jelly roll pan with non-stick cooking spray and set aside.

Combining Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, ground ginger, ground nutmeg, ground cloves, and salt. Ensure these ingredients are well combined and set the bowl aside.

Creaming Butter and Sugars: In a separate large mixing bowl or the bowl of a stand mixer, combine the melted butter, granulated sugar, dark brown sugar, vanilla extract, and molasses. Beat these ingredients on medium speed until the mixture is light and fluffy, approximately 2 to 3 minutes.

Adding Egg and Dry Ingredients: Incorporate the egg into the butter and sugar mixture until thoroughly combined. Gradually add the dry ingredients to the wet mixture, initially mixing on a low speed to incorporate the flour, then increasing to medium speed until the mixture is well combined, approximately 1 minute.

Baking: Transfer the dough into the prepared pan, spreading it evenly. Bake in the preheated oven for 15 to 20 minutes, or until the bars have darkened in color and a toothpick inserted into the center comes out with a few moist crumbs. Remove from the oven and allow to cool completely on a wire rack before frosting.

Creaming Cream Cheese and Butter: In a large mixing bowl or the bowl of a stand mixer, combine the softened cream cheese and butter. Beat on medium speed until the mixture is light and fluffy, approximately 2 to 3 minutes.

Adding Powdered Sugar and Vanilla: Gradually add the powdered sugar and vanilla extract to the cream cheese mixture. Initially mix on a low speed to incorporate the powdered sugar, then increase to medium-high speed, beating until the frosting is creamy and smooth, approximately 1 to 2 minutes.

Frosting and Serving: Once the cookie bars have cooled completely, spread the cream cheese frosting evenly over the top. If desired, decorate with holiday sprinkles. Slice into bars and serve.