Preheat the oven to 325°F (160°C) and line two large baking sheets with parchment paper.
Add the butter, brown sugar, and white sugar to a large mixing bowl. Use an electric mixer fitted with the whisk attachments to beat on high speed, for at least 3-4 minutes, or until light and creamy.
Add the eggs one at a time, beating well between each addition. Add the vanilla and mix to combine.
Sift in the flour, baking soda, and salt. Beat on the lowest speed until just mixed. A few streaks of flour are fine.
Add the chocolate and fold in by hand with a spatula to evenly incorporate.
Scoop even balls of dough onto the prepared baking sheets, 2 tablespoons each. Leave about 2 inches (6cm) between each cookie.
Flatten each ball slightly with a small square of parchment paper and something with a flat bottom (a measuring cup or drinking glass are great) or wet the heel of your hand slightly and use your hands instead.
Bake the cookies for 12-14 minutes, or until the edges are just firm. The cookies won't darken significantly.
Cool fully on the baking sheets before removing and storing.
Repeat until all of the cookie dough has been used up.
Keep the cooking in an airtight container at room temperature for up to three days, or up to a week in the refrigerator. These can be frozen to up to three months.
Notes
If your butter is too soft the cookies may spread. If you’re not sure, and the dough seems really soft, refrigerate it in the bowl for an hour before scooping and baking.