For best results, use a kitchen scale to weigh the ingredients.
Instructions
Combine softened butter with both sugars and vanilla extract in a large bowl or the bowl of a stand mixer. Mix by hand using the "creaming method" with a wide rubber spatula to smear the butter and sugar together and mix vigorously until smooth and slightly fluffed. If you use a stand mixer, secure the paddle attachment and mix on medium-low speed for 2-3 minutes. It should lighten in color and look quite fluffy. You can also use a handheld mixer. Scrape down the sides of the bowl and mix in egg until evenly incorporated. The mixture should look a bit whipped at this point.
Combine flour, baking soda and salt in a medium bowl and whisk to blend evenly. Add this to butter mixture all at once and mix gently until just combined. Add the chocolate and fold it in until evenly distributed.
Cover the dough in the bowl with plastic wrap and refrigerate for 1 hour.
Preheat your oven to 375°F. Lightly grease two large cookie sheets with soft butter (I like to use a spent wrapper from a stick or brick of butter to do this - no waste!).
Use a 1.35-oz cookie scoop to portion dough onto prepared baking trays leaving about 4 inches of space between them since they will spread a lot. You should only have 6 cookies per tray. Do not flatten. Bake for about 10-12 minutes until nicely browned around the edges like the color of copper. The center should be just lightly golden and just started to puff up - that's how you know it won't be completely raw in the middle even though it looks underdone. The center will set as the cookies cool.
Remove trays from oven and transfer to wire racks. Let cookies cool for 2 minutes on trays before transferring individually to the racks to finish cooling.