In a large bowl using a handheld mixer or stand mixer fitted with a paddle attachment, beat the butter, brown sugar, and granulated sugar together on medium-high speed until combined and creamy, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Beat in the egg and vanilla extract on high speed. Scrape down the sides and up the bottom of the bowl as needed, and continue to beat until fully combined. Add the flour and salt and beat on low speed until combined.

Finally, beat in the chosen flavor add-ins (see Notes) on low speed until just combined. Avoid overmixing—blend only until the mix-ins are evenly distributed. The cookie dough will be thick and slightly sticky. If it seems too sticky to roll into logs, beat in 1–2 Tbsp more flour.

Turn the dough out onto a floured work surface and, with floured hands, divide or cut in half. Roll/shape each half into an 8-inch log, about 1.5 to 2 inches in diameter. The measurements don’t have to be exact. Tightly wrap the dough logs in plastic wrap and chill in the refrigerator for at least 4 hours and up to 5 days.

Preheat the oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats. Set aside.

Pour enough coarse sugar on an 8-inch or larger plate to cover it. Roll the logs in the sugar. You may need to really press the dough logs down into the sugar if it’s not really sticking. (I find coating the dough logs in sugar after chilling much easier, as the dough is too sticky to neatly roll in sugar right after mixing.)

Slice each dough log into 12 equally thick cookies and arrange cookies on prepared baking sheets about 2 inches apart.

Bake the cookies for 13–15 minutes or until very lightly brown around the edges (they won’t brown much). Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a cooling rack to cool completely.

Dip or drizzle with melted chocolate and add toppings, if desired. See Flavors in the recipe Notes below.

Cookies will stay fresh covered at room temperature for up to 1 week.