01 -
In the bowl of a stand mixer fitted with a paddle attachment or a large mixing bowl with an electric mixer, beat butter, granulated sugar, and brown sugar on medium-high speed until creamed and well combined, about 2 to 3 minutes.
02 -
Stop the mixer, scrape down the sides of the bowl, and add the egg, milk, rum extract, and spearmint extract. Beat on medium-high speed until light and fluffy, about 2 minutes.
03 -
Stop the mixer, scrape down the sides of the bowl, and add the flour, baking soda, and salt. Mix on low speed until just combined, about 1 minute or less.
04 -
Using a 2-ounce cookie scoop, form approximately 16 uniformly sized cookie dough balls. Place on a large plate or platter, cover with plastic wrap, and chill in the fridge for at least 2 hours or up to 4 days before baking.
05 -
Preheat the oven to 350°F (175°C). Line a baking sheet with a nonstick baking mat or spray with cooking spray. Place the chilled dough balls on the baking sheet, spaced evenly apart, about 8 per sheet. Bake for 10 to 12 minutes, until pale golden and the edges are just set. The centers may appear slightly undercooked and glossy. For firmer cookies, extend baking time by 1 to 3 minutes.
06 -
Allow cookies to cool on the baking sheet for 10 minutes before transferring to a wire rack to cool fully.
07 -
While the cookies cool, garnish with lime zest and fresh mint leaves to taste. Garnished cookies are best consumed within a few hours as the lime zest and mint will discolor over time.