Preheat the oven to 350℉ and lightly grease the edges of a cast-iron skillet with cooking spray or oil.
In a medium, pan over low heat, melt the butter, 1 cup of the chocolate chips, and the unsweetened chocolate until smooth in texture. Stir constantly and set aside to cool for 10 minutes.
In a large mixing bowl whisk the eggs, vanilla, and sugar. Pour the cooled chocolate mixture into the egg mixture and stir until combined.
In a separated medium bowl, whisk together 1/2 cup of flour, baking powder, and salt. Add the chocolate mixture to the dry ingredients and stir to combine.
Toss the 2 tablespoons of flour with the remaining 1 cup of chocolate chips and fold into the chocolate mixture.
Pour the batter into the prepared skillet and place it on top of a baking sheet. Bake for 45 minutes or until a toothpick inserted in the center comes out clean.