Preheat the oven to 375°F. Lightly grease two baking sheets, or line with parchment., Beat together the butter, sugars, vanilla, salt, baking powder, and baking soda till well combined., Add the egg, beating till smooth. Scrape the sides of the bowl, and beat again till smooth., Add the flour, mixing it in completely., If you're making cookies using chips, nuts, etc, beat in the milk, then the add-ins., If you're making plain cookies, without add-ins, omit the milk., Drop the cookies by the traditional "tablespoonful" (actually about 4 measuring teaspoons) onto the prepared baking sheets, spacing them about 2" apart. A tablespoon cookie scoop works well here., Bake the cookies for 10 to 14 minutes (or up to 16 minutes; ovens may vary). The cookies should be a light golden brown, and a bit darker around the edges. For softer cookies, bake the shorter amount of time; for crunchy cookies, bake longer., Remove the cookies from the oven, and cool right on the baking sheets.