Soak the raisins in warm water. Put the flour, sugar, eggs and ricotta in a bowl and quickly mix the ingredients together with a wooden spoon. Add the drained and “dried” raisins, the chocolate broken into small pieces, the Vin Santo and the olive oil, and continue mixing. Finally add the baking powder, stirring it in well. Butter and flour a cake tin measuring about 20 cm in diameter, pour in the mixture and cook in a preheated oven, at 160 °C, for an hour. If the top begins to brown too much, after half an hour cover with kitchen foil and, perhaps, turn down the heat slightly. Serve with fairly runny pastry cream (or zabaglione, or mascarpone), either on the side or “poured” over the top, and a sprinkling of chocolate shavings.