Preheat oven to 375 degrees (best to refrigerate dough overnight before baking). Melt butter, then mix in brown sugar and cream on medium speed with electric mixer. Add the egg, milk, and vanilla and mix. Slowly incorporate the dry ingredients (flour, salt, baking soda) until well blended. Stir in bittersweet chips. Chill the dough at least 2 hours, or overnight. To bake, scoop onto parchment-lined sheets and bake until done, 10-14 minutes (it's not an exact science, I start watching them carefully after 7 or 8 minutes). Cool completely and store in an airtight container.