Place two racks in the upper and lower thirds of the oven and preheat to 350°F. Line two baking sheets with parchment.
In a large bowl, whisk together the flour, baking powder, baking soda and salt.
In another large bowl, cream the butter and sugar with a handheld mixer or stand mixer just until the butter and sugars are blended, about 2 minutes. Use a spatula to scrape down the sides of the bowl. Add the eggs one at a time, mixing until each is combined. Mix in the vanilla.
Add the flour mixture to the bowl and blend on low speed until the flour is barely combined, about 30 seconds. Scrape down the sides and bottom of the bowl.
Add the chocolate all at once to the batter. Mix on low speed until the chocolate is evenly combined. Use a spatula to scrape down the sides and bottom of the bowl and if needed stir and knead the batter to incorporate all of the ingredients.
Scoop mounds of dough -- about 1-2 tablespoons in size -- onto the baking sheets, leaving 3 inches between them.
Bake the cookies for 16 to 20 minutes, rotating the sheets halfway through, until the cookies are evenly dark brown. Note: I baked for 10 minutes, then rotated and baked for 8 more minutes.
Place the baking sheet on a rack for a few minutes, then transfer the cookies to the rack to cool fully. Repeat with the remaining dough. Cookies are best eaten warm from the oven or later that same day. They'll keep in an airtight container for up to 3 days.