Preheat oven to 350 degrees F. Line an 8-inch square metal baking pan with foil and grease the bottom (or use nonstick foil).
In a microwave-safe bowl or 2 cup glass measure, melt the chocolate and butter together at 50% power stirring every 30 to 60 seconds or so. Alternatively, you may do this in a double boiler. Set aside.
In a second bowl, whisk together the flour, baking powder and salt.
In a standing mixer with the whisk attachment (or you can use a handheld mixer), beat eggs. With the mixer going, pour in the sugar and continue beating for 3-5 minutes or until thick and yellow. Beat in the vanilla.
Remove mixer from stand and with a scraper or a big spoon, stir in the melted chocolate mixture, then add flour mixture and stir until blended.
Spread batter in pan and bake for 30 minutes or until brownies appear set and internal temperature registers around 209. Let cool completely, then cover and chill overnight. Lift from pan and cut into 6 large brownies. For medium size brownies, cut to make 12 brownies. For small brownies, cut again to make 24.