Preheat the oven to 350 F. Place a 9” cast iron skillet into the oven with a pat of butter.
In a small bowl, combine the flour, salt and baking powder. In a microwave safe bowl, heat the dark chocolate chips in 30 second intervals, stirring in between. It should take 60-90 seconds to completely melt the chocolate chips. Add the butter in and microwave for an additional 30 seconds. Stir them together.
In a large mixing bowl, whisk together the melted chocolate mixture, brown sugar and sugar. Add in the eggs and mix. Whisk in the vegetable oil and buttermilk. Add the vanilla and stir. Add the cocoa and flour mixture and stir just until incorporated. Fold in the chocolate chips then fold in half of the raspberries.
Take the cast iron skillet out of the oven and spread the butter around. Pour the brownie batter into the skillet. Top with the remaining raspberries. Place into the oven to bake for 40 minutes or until a toothpick inserted comes out clean or with moist crumbs.
Once baked, remove from the oven and place onto a cooling rack to cool for several minutes before cutting and serving.
Storage: Brownies may be stored in an airtight container or baggie at room temp for up to 3 days or in the fridge for up to 5 days.