1-First Step: Mise en Place
Measure all ingredients accurately for success in your copycat Costco chocolate chip cookies. Soften butter to room temperature; it should dent easily but hold shape. Chop chocolate into large chunks if using bars for authentic size. In a medium bowl, whisk flour, baking soda, and salt. This dry mix ensures even distribution, preventing dense spots. For dietary tweaks, use gluten-free flour here without changing other steps.

2-Second Step: Cream Butter and Sugars
Beat softened butter, granulated sugar, and brown sugar in a large bowl with electric mixer on medium speed for 2-3 minutes. Mixture turns light and fluffy, trapping air for tender cookies. Scrape sides often. Add vanilla extract. This base captures the sweet chew of Costco cookies recipe. Vegan note: Vegan butter creams similarly; chill dough if too soft.

3-Third Step: Incorporate Eggs
Add eggs one at a time, beating well after each (about 1 minute). Dough looks smooth and glossy. Eggs add moisture and richness, key for giant chocolate chunk cookies. If using flax eggs for vegan, mix in now; they gel for binding.

4-Fourth Step: Combine Wet and Dry
Gently stir dry ingredients into wet on low speed until just combined. Avoid overmixing to keep cookies soft. Dough will be thick. Fold in chocolate chunks by hand for even distribution. Taste a tiny bit; adjust salt if needed. For low-calorie, add chunks sparingly.

5-Fifth Step: Scoop and Chill
Use a 1/4-cup ice cream scoop for 5-7 ounce balls, like food court style. Place 6 per sheet, 3 inches apart; they spread. Chill dough 30 minutes (or overnight) for better shape. This step mimics professional techniques for gourmet chocolate chunk cookies.

6-Sixth Step: Bake
Bake 12-15 minutes until edges golden, centers soft. Rotate sheets halfway. Cool on sheet 5 minutes, then wire rack. They firm up for chewy texture. High altitude: add 2 tbsp flour, bake 10-12 min.

7-Final Step: Finishing Touches and Serving
Sprinkle sea salt on warm cookies for contrast. Serve with milk or ice cream. Store as below. These shine at parties; busy parents love make-ahead scoops.