Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper (or a silicone mat)—this helps cookies bake evenly and release easily.

In a medium bowl, whisk together flour, baking soda, salt, and cornstarch. Pro tip: sift once for lump-free dough, especially if your flour is prone to clumps.

In a large bowl or stand mixer fitted with the paddle attachment, beat softened butter, granulated sugar, and brown sugar on medium speed until fluffy and pale, about 2–3 minutes. Scrape down the sides with a spatula so everything mixes evenly.

Crack in the egg and extra yolk, then pour vanilla. Beat on low until just combined—overmixing can lead to flatter cookies.

Gently fold in the flour mixture with a spatula or on low mixer speed until you no longer see streaks of flour. The dough should feel soft but not sticky.

Use a wooden spoon to fold in chocolate chips until they’re evenly distributed. If you’re adding nuts, toss them in now, too.

Cover the bowl with plastic wrap and chill in the fridge for at least 30 minutes—or up to 48 hours for a deeper, bolder flavor.

Use a 2-tablespoon cookie scoop or roll dough into balls and place on prepared sheets. Bake for 10–12 minutes until set but still soft in the center. Cool before enjoying.