In a large bowl, using a wooden spoon, cream together the butter and brown and granulated sugars until smooth but not over mixed. (I do this by hand, but if you use a stand mixer fitted with the paddle attachment or a handheld mixer, beat on medium speed for 1 to 2 minutes, and then scrape down the sides of the bowl before continuing.) Add the egg, vanilla and salt and stir just until combined.
Sift in the flour, baking soda and baking powder and stir gently just until combined. Add the chocolate and nuts if using and stir just until evenly distributed throughout the dough. Cover and refrigerate for 30 minutes.
Position the racks in the upper third and lower third of the oven and preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper.
Scoop up 1-inch balls of the dough with a spoon or mini scoop and set them 2 inches apart on the prepared pans. Bake the cookies, rotating the pans after 7 to 9 minutes, for 13 to 17 minutes until the cookies are golden brown. If you like a very soft cookie, bake them for 13 minutes. If you like a crisp cookie, bake them for 17 minutes. Transfer to racks and let cool. I think these cookies are best the day they are baked, but they will keep in an airtight cookie jar for up to 4 days-if they last that long.