Do not overmix your butter and sugar. Stop when the mixture has slightly paled in color and starts sticking to the sides of the bowl.
Keep your eggs cold. This will keep the butter in your dough from getting too warm.
Use chopped chocolate instead of chocolate chips. Chocolate chips are made to hold their shape as they bake, whereas roughly chopped chocolate with melt into the dough. Also, you can use higher quality chocolate bars resulting in superior taste (and fewer additives).
Let the dough rest overnight (at least 12 hours and up to 72 hour) before baking for better flavor and texture. Yes, it really does make a difference!
Take the cookies out of the oven when the edges appear browned but the center isn’t quite set. Leave the cookies on the baking sheet for 5 minutes to finish cooking, then transfer to a wire rack to cool completely. You’ll get crisp edges and chewy centers every time.
If your cookies come out of the oven a little lopsided, immediately use a spatula to press the hot cookie back into a perfect circle.