Preheat oven to 350 degrees F. Lightly grease a 9x13 inch metal pan or line it with foil and grease the bottom.

In a microwave-safe mixing bowl, or in a saucepan set over low heat, melt the butter, then add the sugar and stir to combine. Return the mixture to the heat (or microwave for 1 minute) and heat until mixture is very hot but not bubbling; it'll become shiny looking as you stir it. Heating the butter and sugar a second time will dissolve more of the sugar, which will yield a shiny top crust on your brownies.

Transfer the mixture to a bowl (if you melted the butter and sugar in the mixing bowl, you don't have to transfer anything).Stir in the cocoa, salt, baking powder and vanilla. Add the eggs, beating till smooth; then add the flour and chips, stirring until combined. (Note: if the batter is still very warm, let it cool slightly before adding the chips, otherwise they will melt into the batter).

Spoon the batter into the prepared pan.

Bake the brownies for 28 minutes, until a cake tester inserted into the center comes out dry. Remove them from the oven and after 5 minutes, loosen the edges with a table knife. This helps prevent sinking as they cool. Cool completely (and chill for better cutting) then cut and serve.