Line bottom of a jelly roll pan ( 15.5 x 10.5 x 3 cm) with baking parchment and grease sides of pan. Mix kahlua and coffee crystals. Melt chocolate, butter and shortening together over very low heat, and cool slightly. Beat eggs lightly, add sugar and continue beating until thick and light colored. Slowly stir in kahlua and chocolate mixtures. Resift flour with baking powder and salt into batter, and mix until smooth. Turn into prepared pan and level top. Sprinkle nuts evenly over top. Bake on center rack of 350 degree oven, about 25 minutes, just until cake tests dome. Cool in pan on wire rack. To serve...cut into small 4 cm squares or sieve powdered sugar over top and cut. Or, cut into 6 cm squares and serve tipped with ice cream and drizzle of chocolate sauce. Or, for a more lavish dessert, put 2 of the larger squares together with ice cream between and top with a rosette of whipped cream.