In medium bowl, combine flour, cocoa, soda and salt. Mix well with a wire whisk.
Blend sugars in a large bowl using an electric mixer set at medium speed.
Add butter and mix to form a grainy paste, scraping down the sides of the bowl. Add eggs and vanilla, and beat at a medium speed until smooth. Add the flour mixture and chocolates, and blend at low speed until just combined. Do not over-mix. Bake 23-25 minutes.