Adjust the oven rack one-third up from the bottom and preheat oven to 350F. Prepare a shallow 8-inch square metal baking pan lined with foil that has been smoothed into place. Butter the foil using soft or melted butter and a pastry brush. Set the prepared pan aside.
Place the chocolate in the top of a small double boiler over hot water on low to moderate heat. Cover until partially melted, then uncover and stir until completely melted and smooth. Remove the top of the double boiler and set aside, uncovered, to cool slightly. Do not let the water come in contact with the chocolate.
The almonds must be ground to a fine powder. It may be done in a food processor, a nut grinder, or a blender. Set aside.
In the large bowl of an electric mixer cream the butter. Add the coffee, vanilla, rum, and the melted chocolate and beat until smooth. Add the egg yolks all at once and beat until smooth. Add the flour and then the almonds and beat until incorporated. Remove from the mixer.
In the small bowl of the electric mixer add the salt to the egg whites and, with clean beaters, beat only until the whites barely hold a firm shape, not until they are stiff or dry.
Gradually, in several additions, small at first, fold the whites into the chocolate mixture. Be careful not to overmix - you don't want the whites to deflate.
Turn into the prepared pan and smooth the top.
Bake for 30 minutes.
Cool in the pan for about 15 minutes.
Cover with a rack and invert. Remove the pan and foil, cover with another rack and invert again, leaving the cake to cool right side up. (The cake will be a scant 1 inch high.)
Place the remaining chocolate and butter in the top of a small double boiler over hot water on low to moderate heat. Cover until partially melted. Then uncover and stir until completely melted and smooth. Stir in the coffee. If the mixture is not smooth, stir it briskly with a small wire whisk. Remove from the hot water and set aside to cool to room temperature.
Then let stand at room temperature or refrigerate, stirring occasionally, until only slightly thickened or thick enough so it will spread without running down the sides.
Place the cake upside down on a small board.
When the icing is ready, stir it well and turn it out onto the cake. With a long, narrow metal spatula spread smoothly.
Let stand until the icing is set (it will not take long).
After the cake is cut into squares they may be served as they are, or each one may be topped with a walnut or pecan half, a whole, toasted blanched hazelnut, or a chocolate covered espresso bean.
If you plan to leave them plain, when the icing is set use a long, thin, sharp knife to trim the edges and then cut the cake into 16 small squares.
To store these overnight or to freeze them, pack in a single layer in a box or on a tray. Cover the squares airtight with plastic wrap. If you have frozen them, thaw before unwrapping.
Makes 16 squares
Prep Time: 30 mins.
Cook Time: 60 mins.