📖 Instructions

1. Preheat your oven and prepare the pan: First things first, get that oven preheated to 350°F (175°C). While it's heating up, grab a 9x13 inch baking pan. Line it with parchment paper, making sure to leave an overhang on the sides. This little trick will make it so much easier to lift the whole cookie slab out later. Trust me, you'll thank yourself for this step! If you don't have parchment, lightly grease and flour the pan, but parchment is definitely the way to go for easy removal.
2. Cream butter and sugars: In a large mixing bowl, or the bowl of a stand mixer fitted with the paddle attachment, combine your softened unsalted butter with both the granulated sugar and light brown sugar. Beat these together on medium speed until the mixture is light, fluffy, and looks pale in color. This usually takes about 2-3 minutes. This step is super important for the texture of your cookies; it whips air into the butter and sugar, which contributes to that lovely chewiness.
3. Add eggs and vanilla: Next, crack in both large eggs, one at a time, beating well after each addition until fully incorporated. Then, pour in the vanilla extract. Scrape down the sides of the bowl with a rubber spatula to make sure everything is evenly mixed. Don't be shy with that vanilla! It really enhances the chocolate flavors.
4. Combine dry ingredients: In a separate, medium-sized bowl, whisk together the all-purpose flour, baking soda, and a pinch of salt. Give it a good whisk to ensure the leavening agents and salt are evenly distributed throughout the flour.
5. Gradually add dry to wet: With your mixer on low speed, slowly add the dry ingredient mixture to the wet ingredients, a little at a time. Mix just until *barely* combined. You don't want to overmix at this stage; overmixing can develop too much gluten, resulting in a tougher cookie slab. Stop as soon as you see no more streaks of dry flour.
6. Fold in the chips: This is the fun part! Add your semi-sweet chocolate chips, milk chocolate chips, and white chocolate chips to the dough. Using your rubber spatula, gently fold them in until they are evenly distributed throughout the dough. Try not to crush them. Make sure those chips are everywhere so every bite is packed with goodness!
7. Press into the pan: Now, spoon the glorious cookie dough into your prepared 9x13 inch baking pan. Using the back of your spatula or your clean hands (lightly dampened if the dough is sticky), press the dough evenly into the pan. Make sure it reaches all the corners and has a consistent thickness across the entire surface. This ensures even baking.
8. Bake to perfection: Place the pan in your preheated oven. Bake for about 25-30 minutes. The edges should look golden brown, and the center should still look a little soft or slightly underbaked. Remember what I said about not overbaking? Trust your gut here! If you want that super chewy middle, pull it out when it looks just set, not deeply golden all over.
9. Cool before cutting: Once out of the oven, let the cookie slab cool in the pan on a wire rack for at least 30 minutes, or even an hour. As it cools, it will continue to set up, and the chocolate will firm up slightly. This makes it much easier to cut neat squares. If you try to cut it too soon, it might be too crumbly and messy, though still delicious of course!
10. Lift, slice, and enjoy: Once sufficiently cooled, use the parchment paper overhang to carefully lift the entire cookie slab out of the pan and onto a cutting board. Use a sharp knife to cut it into squares, rectangles, or whatever shape your heart desires. Serve them warm or at room temperature. They're amazing with a cold glass of milk, a hot cup of coffee, or a scoop of ice cream!