Yield: 6-8 servings. Preheat oven to 200 0C / 400 0F / Gas 6. Grease and line an 18 x 28 cm (7 x 11 inch) Swiss roll tin. Put the eggs and sugar in a large bowl and stand it over a pan of hot water. Whisk together until doubled in volume and thick enough to leave a thin trail on the surface when the whisk is lifted. Fold in 1 tablespoon of the coffee essence and the walnuts. Pour the mixture into the prepared tin and bake for 8-10 minutes until risen and firm to the touch. Place a sheet of greaseproof paper over a damp tea-towel. Quickly turn out the cake on to the paper and trim the edges. Roll up the cake with the paper inside. Leave to cool for about 30 minutes, covered with the damp tea-towel. Whisk the cream until stiff, then fold in the remaining coffee essence. When cold, unroll the coffee log and remove the paper. Gently spread with the filling and re-roll. Do not worry if it cracks slightly. Dust with icing sugar before serving.