Preheat the oven to 325 degrees F and line a rimmed baking sheet with parchment.
Remove the stems from the kale and spread the leaves on the prepared baking sheet. Roast, rotating the baking sheet halfway through, until dry, 20 to 25 minutes. Transfer the kale to a food processor and grind into a powder. You should have about 3/4 cup.
Beat the butter and sugar in a stand mixer with the paddle attachment on medium-high speed until light and fluffy, 3 to 5 minutes. Add the egg, mint, salt and baking powder and beat, scraping down the bowl as needed, until fully combined. Reduce the mixer speed to low; add the flour and ground kale and beat until fully combined. Cover with plastic wrap and refrigerate until firm, about 1 hour.
Position the oven racks in the upper and lower thirds of the oven and preheat the oven to 350 degrees F. Line 2 baking sheets with parchment and butter the parchment. Using a teaspoon measure, scoop the dough and form into small balls. Arrange the balls about 2 inches apart on the prepared baking sheets. Bake, switching the baking sheets halfway through, until the edges of the cookies are golden brown, 15 to 20 minutes. Let the cookies cool for 1 minute on the baking sheets before carefully transferring to a cooling rack to cool completely.
Fill a medium saucepan with 2 1/2 cups water and bring to a simmer. Place a medium heat-proof bowl over (not in) the water and add the chocolate chips. With a heat-proof spatula, stir the chocolate chips until fully melted. Drizzle the cookies with the chocolate or dip them in the bowl. Let set before serving.