Mystery Cookie Recipe

Preheat and prepare

Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone mats. If using, brush sheets lightly with melted butter or leave parchment in place.

Measure out and set aside mix-ins so they are ready when the dough is mixed.

Cream butter and sugars

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

Add egg and vanilla

Add the large egg and vanilla extract and beat on low to combine, then increase to medium-high and beat for about 30 seconds until smooth and slightly aerated.

Combine dry ingredients

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

With the mixer on low speed, add the dry ingredients to the butter mixture in two additions, mixing just until combined and no streaks of flour remain. Do not overmix; scrape the bowl once and finish folding by hand if necessary.

Fold in mystery mix-ins

Remove the bowl from the mixer and fold in the semisweet chocolate chips plus the chosen optional mix-ins (toasted chopped walnuts and/or dried cherries/raisins) using a rubber spatula. Ensure the mix-ins are evenly distributed so every cookie has a bit of each.

Portion the cookies

Using a 1.5 tablespoon scoop (or a tablespoon if you prefer smaller cookies), portion dough about 1.5 tablespoons per cookie and place dough balls 2 inches apart on the prepared baking sheets. For a uniform look, roll each portion into a smooth ball between your palms.

If you like slightly flatter cookies, press each dough ball gently with the palm to flatten by about one-third. For taller, chewier cookies leave them rounded.

Bake

Bake one sheet at a time in the preheated oven for 9–12 minutes, rotating the sheet front-to-back halfway through. Cookies are done when edges are golden and centers still look slightly soft. Thinner cookies take closer to 9 minutes; thicker ones closer to 12.

Cool and salt

Remove the cookies from the oven and let them cool on the baking sheet for 4–5 minutes to set. While still warm, sprinkle a tiny pinch (a few grains) of coarse sea salt on top of each cookie if desired. Transfer cookies to a wire rack to cool completely.

Repeat with remaining dough. Store cooled cookies in an airtight container at room temperature for up to 4 days, or freeze for up to 3 months.