Whisk together flour, baking powder, and salt in a medium bowl. Set aside the flour mixture.

Cream butter and dark brown sugar in the bowl of a stand mixer fitted with the paddle attachment or in a large bowl with a hand mixer (or electric mixer) on medium speed until a paste forms. Add egg and vanilla extract, and beat well to combine. 

Reduce the mixer to low and add dry ingredients in three additions, waiting until almost all the flour has been incorporated before adding the next. 

Preheat the oven to 325°F convection (with fan) or 350°F conventional (no fan).

Place the cookie dough balls 2 inches apart on a cookie sheet lined with parchment paper or a silicone mat. Bake in a preheated oven for 17-20 minutes (from frozen for a 13 cookie yield) until the edges are a nice golden brown, the centers have puffed and the surface looks matte not shiny. Cool completely. You can cool them on a wire rack or on the baking pan.