Preheat the oven to 350 degrees. Line a cookie sheet with parchment paper (or grease the sheet lightly). Melt the butter and chocolate together in the top part of a double boiler. Remove the pan from the heat and set aside to let ingredients cool. Sift the flour, salt and baking powder together in a bowl and set aside. Beat the eggs, egg yolk, sugar and brown sugar in the bowl of an electric mixer set at medium speed, until well blended, about 5 minutes. Fold the cooled chocolate mixture into the egg mixture until thoroughly blended. Add the flour mixture and blend in thoroughly. Let the batter rest for 10 minutes. Use a 2-ounce scoop to form a rounded mound and place on the prepared cookie sheet. Leave space between the cookies for expansion. Bake for 15-17 minutes. OR makes smaller (one ounce) cookies and bake for 10-12 minutes. Cookies should be cracked, with moist looking ingredients inside the cracks. Makes 12-24 cookies depending on size