Simmer the dates in a saucepan with the 150 ml (¼ pint) boiling water, covered, for 5 minutes until softened. Gradually mix the cocoa powder in a bowl with the remaining 6 tablespoons boiling water until smooth. Leave the dates and dissolved cocoa powder to cool.
Add the oil, eggs and sugar to the dissolved cocoa powder then whisk together until smooth. Add the flour and baking powder then whisk again. Stir in the cooled dates and any cooking liquid and mix well.
Divide the mixture evenly between 2 x 20 cm (8 inch) sandwich tins, greased and base-lined with oiled greaseproof paper, and spread the surfaces level. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes until well risen and the cakes spring back when gently pressed with a fingertip.
Leave to cool in the tins for 5 minutes then loosen the edges, turn out on to a wire rack and peel off the lining paper. Leave to cool completely.
Whip the cream until softly peaking then fold in the fromage frais. Put one cake on to a serving plate, spoon over chocolate spread then half the cream. Top with the second cake and spread with the remaining cream. Decorate with the halved chocolate truffles.