1. Whisk flour, baking powder, baking soda, and salt in a medium bowl until combined; set aside. In a large bowl, combine butter and both sugars and beat with an electric mixer on medium-high until very light and fluffy, about 4 minutes. Scrape down bowl, then add egg and egg yolk, vanilla, and nutmeg (if using) and continue to beat until very smooth, about 2 more minutes. Scrape bottom and sides of bowl, add dry ingredients, and mix on low until just combined; gently fold in chocolate. Cover bowl and refrigerate dough for at least 30 minutes and up to 1 day.
2. When ready to bake, place racks in upper-middle and lower-middle of oven and heat to 375 degrees. Line two baking sheets with parchment paper.
3. Gently roll 1/4-cup portions of dough into balls and place on prepared baking sheets, spacing cookies 2" apart. Using your hands, gently flatten dough balls to a 3/4" thickness, then sprinkle each with a pinch of flaky salt (if using).
4. Bake until cookies are puffed and edges are golden but centers appear slightly underdone, 13 to 15 minutes, rotating and switching pans midway through (cookies will finish cooking as they cool).
5. Cool 5 minutes on baking sheets, then transfer cookies to wire racks and cool at least 10 more minutes. Enjoy warm, or cool completely and store in an airtight container at room temperature for up to 2 days.
Source: Hannaford fresh Magazine, January - February 2020