Preheat oven to 300 degrees. Line 2 rimmed baking sheet with parchment paper. Whisk flour, cocoa, baking powder, baking soda and salt together in a bowl. Set aside. Microwave 6 ounces chocolate, oil and butter in medium bowl at 30 second intervals, stirring Each time you restart the microwave. When melted, whisk milk, half-and-half or heavy cream into chocolate mixture until combined. Using a stand mixer, whip sugar and eggs on medium high speed until very pale, about 4 minutes. Add melted chocolate mixture and whisk by hand until thoroughly combined. Fold in flour mixture with spatula until thoroughly combined and no dry pockets remain. Fold in remaining 4 ounces of chocolate. Spoon 10 heaping tablespoon portions of batter onto each prepared sheet. You should have 20 total cookies.) Bake until cookies are puffed and covered with a large cracks, About 15 minutes.( Cookies will look raw in between the cracks and eventually flatten). Allow cookies to cool completely on the sheet pans, then slide a thin spatula under the cookies to remove from the sheets. To keep cookies soft, store in an airtight Ziploc bag or airtight container. Cookies can be frozen.