Pre-heat the oven to 350°F and grease your choice of a pie plate or a 9-inch springform pan.
Melt the butter and 2 cups of chocolate chips in either a heat-safe bowl until smooth, using either a double boiler or the microwave on 50% power in 30-second intervals.
Allow the mixture to cool slightly.
In an electric mixer, on medium-high, whip the eggs, sugar and vanilla extract for about 3 minutes until the mixture is light and fluffy.
Stir the cooled chocolate mixture into the egg mixture.
Gently fold in the flour, baking powder and salt until just combined; then stir in the remaining 1 cup of chocolate chips.
Pour the batter into the prepared pan, place in the pre-heated oven and bake for 35 – 40 minutes, or until the center has puffed up and the top may crack.
Allow the pie to cool completely before topping with hot fudge to serve.
