STEP 1: PREHEAT THE OVEN

Preheat your oven to 350°F (175°C) and line a 9×13-inch baking pan with parchment paper. If you don’t have parchment paper, you can lightly grease the pan with butter or nonstick spray, but parchment paper will make removing the bars easier once they’ve cooled.

STEP 2: MIX THE DRY INGREDIENTS

In a medium-sized bowl, whisk together the flour, baking powder, and salt. This ensures that the baking powder is evenly distributed, which helps the bars rise uniformly. Set this mixture aside while you work on the wet ingredients.

STEP 3: CREAM THE BUTTER AND SUGARS

In a large bowl, beat together the softened butter, granulated sugar, and brown sugar using an electric mixer or stand mixer on medium speed. Mix until the ingredients are light and fluffy, about 2 minutes. The fluffy texture helps the cookie bars maintain a soft, chewy texture.

STEP 4: ADD EGGS AND VANILLA

Add the eggs, one at a time, beating well after each addition. Then, add the vanilla extract and continue to mix until everything is well incorporated. The eggs provide structure and moisture to the cookie bars, while the vanilla enhances the overall flavor.

STEP 5: COMBINE THE DRY AND WET INGREDIENTS

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix, as this could result in dense bars. You want the dough to come together without being overworked.

STEP 6: FOLD IN THE CHOCOLATE CHIPS AND ADD-INS

Once the dough is mixed, fold in the semi-sweet chocolate chips, white chocolate chips, and any holiday-themed add-ins such as M&M’s or sprinkles. This is the fun part—feel free to add extra candy pieces or even chopped nuts, like pecans or walnuts, if you like a bit of crunch in your cookie bars.

STEP 7: PRESS THE DOUGH INTO THE PAN

Transfer the cookie dough into the prepared 9×13-inch baking pan. Use a spatula or your hands to evenly press the dough into the pan, spreading it out to the edges and smoothing the top. The dough may be a little thick, but that’s okay—it will bake perfectly once it’s in the oven.

STEP 8: BAKE THE COOKIE BARS

Place the pan in the preheated oven and bake for 30–35 minutes, or until the bars are golden brown around the edges and a toothpick inserted into the center comes out clean or with a few moist crumbs. The top of the bars should be slightly puffed, and the edges will begin to pull away from the sides of the pan.

STEP 9: COOL AND SLICE

Once baked, remove the pan from the oven and allow the cookie bars to cool in the pan for about 20 minutes. After they’ve cooled slightly, use the parchment paper to lift the bars out of the pan and onto a cutting board. Allow them to cool completely before slicing them into squares or rectangles.