Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats. If making 2 dozen, have both sheets ready; if 1 dozen, you will use one sheet and keep extras chilled.

Cream butter and sugars

In a large mixing bowl, beat the softened butter, granulated sugar, and light brown sugar together with a hand mixer or stand mixer on medium speed until light and fluffy, about 2–3 minutes. Scrape down the bowl as needed.

Add egg and vanilla

Add the egg and vanilla extract to the butter-sugar mixture and beat until fully incorporated, about 30 seconds. The mixture should look smooth and slightly glossy.

Combine dry ingredients

In a separate bowl, whisk together the all-purpose flour, baking soda, and sea salt until evenly combined.

Mix dry into wet

Gradually add the flour mixture to the wet ingredients in two or three additions, mixing on low speed until just combined. Do not overmix; stop when there are no visible streaks of flour.

Fold in chips and mix-ins

Using a spatula, fold in the semisweet chocolate chips and any chosen optional mix-ins (nuts, oats, dried fruit, white chocolate chips). Ensure they are evenly distributed.

Portion the dough

Scoop the dough into approximately 12 evenly sized portions for 1 dozen (about 2 tablespoons or 30–36 g each). For 2 dozen, scoop 24 portions. Roll each portion gently into a ball and place on the prepared baking sheets 2 inches apart to allow spreading.

Optional chill

For thicker cookies and deeper flavor, chill the dough balls on the baking sheet or in a container for 30–60 minutes before baking. If short on time, proceed directly to baking.

Bake

Bake in the preheated oven for 10–13 minutes for soft, chewy cookies, or 13–16 minutes for crispier edges. Bake until edges are lightly golden and centers still look slightly soft — they will continue to set as they cool.

Finish and cool

Remove the cookies from the oven and, while still warm, optionally sprinkle a tiny pinch of coarse sea salt on each cookie. Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.

Packaging and Yield

Yield: 1 dozen (approx. 12) cookies using the listed ingredient quantities. To produce 2 dozen, double all ingredient quantities and use two baking sheets or bake in batches. Once cooled, stack cookies in a box with parchment or tissue between layers to form a neat box of cookies. Cookies will stay fresh at room temperature in an airtight container for up to 4 days or frozen for up to 3 months.