In a double boiler over simmering water, melt the bittersweet chocolate and butter stirring constantly. In a large mixing bowl, whisk together the sugar, eggs, vanilla extract, and salt. In a separate bowl, sift together the flour and baking powder.
Combine the chocolate, flour, and egg mixtures together. Stir in the white chocolate and hazelnuts.
Rest the dough in the refrigerator until it begins to set up but is still soft enough to spoon out.
Using 2 spoons, drop 1 tablespoon portions of dough 2 inches apart on a parchment paper-lined sheet pan.
Bake for 12 minutes. Cool on the sheet pan for 10 minutes, then transfer to a wire rack to cool completely.
