Heat oven to 350 degrees. Place rack in the middle position. Line cookie sheets with foil or baking parchment.
Microwave the first three ingredients in a medium bowl on high for one minute. Stir well. Repeat at 30-second intervals until mixture is almost completely melted. Stir until melted and smooth.
In another medium bowl, beat eggs, sugar, cocoa, vanilla, salt, and baking powder on high speed until light and bubbly, about two minutes. Reduce speed to low. Beat in the chocolate mixture. Add flour. Beat just until blended. Stir in chips and nuts. Chill dough for 15minutes.
Drop dough onto cookie sheets using about 3tablespoons for each cookie. Leave room for them to spread. Bake 10-12minutes, no longer. The surface will be dry, shiny, and crackled. The inside will be soft. Slide foil or parchment off the cookie sheet and onto a countertop. Cool cookies, then remove to a wire rack. Do not remove from the foil until they are cool or they will fall apart.
Store in an airtight container. Will last up to a week but don’t expect to have any that long.