In a medium mixing bowl, cream the butter and sugars until well blended. Add the egg whites and vanilla, and mix until fully incorporated.
Sift together the flour, baking powder, and salt. Working in batches, add the flour mixture to the sugar mixture. Mix until just incorporated. Add 1/4 cup of each chocolate chip, and mix into the batter.
Grease a 8 x 8- inch baking pan. Spread the batter evenly into the baking pan. Sprinkle the remaining 1/2 cup of chocolate chips evenly on top of the mixture. Bake for 25 minutes, or until a toothpick comes out clean. Allow the blondies to cool in the pan on a wire rack before slicing.