Preheat oven to 350 degrees Fahrenheit and place rack in the middle section of the oven. Line 2 baking sheets with parchment paper and set aside. In a medium bowl combine the flour, salt, and baking powder. Set aside. Place a small pot of water on the stove over low heat. Bring it to a simmer. Over the pot of simmering water, place a stainless steel bowl. Add the chocolate chips and butter, stirring occasionally until completely melted, smooth, and looks like pudding. Set aside to cool slightly. Once the chocolate/butter mixture melts, add the peppermint oil (or extract), stir to combine, and set aside. In a bowl of an electric mixer fitted with a whisk attachment combine eggs, sugars, and cocoa powder. Mix on high until the mixture has doubled in volume and is very very thick, about 4-5 minutes. Reduce the speed to medium and add the melted chocolate/peppermint mixture to the eggs/sugar mixture and mix until combined. Add in the vanilla extract. Reduce the speed to low and add flour mixture all at once. Mix until just combined. It's ok to see some dried flour bits at this point. Fold in the milk chocolate chips. With a cookie scoop (or a teaspoon), drop spoonfuls of dough onto prepared baking sheets. Bake for 8 minutes, rotating the pan halfway through for even baking. Tops of cookies should appear crackled, but the interior will be soft and under-baked.