Preheat the oven to 350F.
In the bowl of a food processor fitted with the blade attachment, pulse the butter and brown sugar until well blended. Add the egg and vanilla and process for a good minute, until the mixture is pale and creamy. Scrape down the sides of the bowl if you need to.
Add the flour, baking soda and salt and pulse until almost combined; add the chocolate chips (and pecans, if you're using them) and pulse just until the dough comes together.
Press the dough into 1 large or 2 smaller cast iron skillets (or bake some of the dough in a skillet and drop the rest by the spoonful onto a parchment-lined sheet); bake for 15-20 minutes, or until pale golden and just set. (If you're baking cookies, bake them for 12-14 minutes, until pale golden around the edges and just set.)