In a heatproof bowl over a double boiler, melt chocolate and butter until smooth. Turn off the stove and let chocolate sit over warm water. Combine flour, baking powder and salt and mix to combine. In another bowl, mix together sugar and eggs, whisk thoroughly and slowly add the warm chocolate mixture. Stir to combine. Mix in vanilla extract. Stir in flour mixture. Allow to cool for a few minutes (if batter is warm, chocolate chips will melt). Stir in chocolate chips. Chill for 10-15 minutes.