En [Note: Instead of the unsweetened chocolate, I just used an extra 4ozs of plain chocolate, and got perfect results. I think as long as you're using *really* good plain chocolate, say at least 55% cocoa solids, it doesn't really matter!]
Preheat the oven to 325F / 170 °C / Gas 3.
Sift together the flour, cocoa powder, bicarbonate of soda, and salt. Set aside.
Heat 1 inch of water in the bottom half of a double boiler over medium heat. Place the plain and the unsweetened chocolates in the top half of the double boiler. Tightly cover the top with cling film and allow to heat for 12 to 15 minutes. Remove from the heat and stir until smooth. Keep at room temperature until needed.
Place the soft light brown sugar and butter in the bowl of an electric mixer fitted with a paddle. Beat on medium for 1 minute. Scrape down the bowl and beat on high for an additional 30 seconds. Scrape down the bowl. Add the eggs, one at a time, while beating on medium, and stopping to scrape down the bowl after incorporating each addition. Add the vanilla essence and beat on medium for 30 seconds. Add the melted chocolate and beat on low for 10 seconds more. Scrape down the bowl and beat for an additional 30 seconds. Add the sifted flour, cocoa powder, bicarbonate of soda, and salt, and the chocolate chips, and beat on low until thoroughly combined - about 20 to 30 seconds. Remove the bowl from the mixer and mix thoroughly with a rubber spatula.
Portion 6 to 8 biscuits per baking sheet by dropping 2 level tablespoons of batter per biscuit onto each of 2 non-stick baking sheets. Place the biscuits on the top and middle shelves of the preheated oven and bake for 18 to 22 minutes, rotating the sheets from top to bottom about halfway through the baking time. Allow the biscuits to cool for 5 to 6 minutes on the baking sheets. Transfer the biscuits to a cooling rack to thoroughly cool before storing in a sealed plastic container. Repeat this procedure until all the biscuits have been baked.
Makes 3 to 3.5 dozen biscuits
>From Marcel Desaulniers' "Death By Chocolate"