1-First Step: Preheat and Prep Heat oven to 350°F (175°C). Grease a 9×13-inch pan or line with parchment for easy removal. Room-temp butter creams best, so set it out early. This setup ensures even baking and clean slices.

2-Second Step: Cream Wet Ingredients In a large bowl, beat 1 cup softened unsalted butter, 1 cup granulated sugar, and 1 cup packed brown sugar. Mix 2-3 minutes until light and fluffy. This incorporates air for tender bars. Scrape sides often. Add 2 large eggs one at a time, beating well after each. Stir in 2 teaspoons vanilla extract. Wet mix should look smooth and pale. Avoid overmixing to keep bars soft.

3-Third Step: Combine Dry Ingredients In a separate bowl, whisk 2 ¼ cups all-purpose flour, 1 teaspoon baking soda, and 1 teaspoon salt. Dry mix prevents lumps. Spoon flour into cup and level for accuracy, avoiding dense results. Gradually add dry to wet, stirring on low speed or by hand. Mix just until combined, no dry streaks. Dough will be thick.

4-Fourth Step: Fold in Chocolate Chips Gently fold in 2 cups semisweet chocolate chips. Use spatula for even distribution. Reserve a handful to press on top before baking for extra chocolatey surface. For brown butter chocolate chip cookie bars, melt and cool butter first: cook over medium until golden and nutty, then chill 20 minutes before creaming.

5-Fifth Step: Spread and Bake Transfer dough to pan, spread evenly with offset spatula. For thick chocolate chip cookie bars, press firmly. Bake 25-30 minutes. Edges golden, center set. Toothpick test: moist crumbs okay, not batter. Rotate pan midway if oven uneven. Ovens vary; check at 25 minutes. Overbaking dries them out.

6-Final Step: Cool and Cut Cool in pan on wire rack 30 minutes. Full cooling firms for slicing. Lift parchment, cut into 24 bars. Enjoy warm or room temp. Store as below.