Preheat oven to 350 degrees F.

In a large, heat-proof bowl over simmering water, melt butter, 1/2 cup chocolate chops and chopped, unsweetened chocolate until smooth. Set aside and let cool for 15 minutes.

In a large bowl stir together the eggs, vanilla and sugar. Stir the chocolate mixture into the egg mixture until well combined.

In a medium bowl, sift together 1/4 cup flour, baking powder and salt and add to the chocolate mixture, stirring until just combined. In a small bowl, toss together the remaining 1/2 cup chocolate chips and one tablespoon flour and fold them into the chocolate mixture. Divide batter into two 6" cast iron skillets or five 3 1/2" cast iron skillets. Place on baking sheet and bake 25 - 35 minutes (depending on skillet size), taking care to not over bake.

If desired, top warm brownies with ice cream and other toppings for a delicious sundae.