Set oven temperature: 210°C for non-fan and 190°C for fan ovens.
Grease and flour the baking pan (I prefer to use a non-stick spray)
Sift the flour, baking powder, bicarbonate of soda and salt together in a bowl and set it aside.
In a food mixer bowl add the butter, olive oil, lemon and orange zest and vanilla and mix at high speed for about 2 minutes, until it is light and fluffy.
Add the eggs one at a time, beating thoroughly after each addition.
Reduce the mixer speed to low and add a third of the flour mix, followed by half of the wine. Repeat with the remaining flour and wine, finishing with the final third of flour. Continue mixing at low speed just to combine the ingredients. Do not be tempted to over mix at this stage.
Pour the mixture into the prepared cake tin. Sprinkle 100g grapes on top.
Place in oven and bake for 20 minutes
Make the sugar crust topping while the cake is in the oven.
Place the butter and sugar in a small bowl and beat with a wooden spoon or electric mixer to form a thick paste.
After 20 minutes gently remove the cake from the oven and dot the sugar crust on top, breaking it into small pieces as you go.
Scatter 100g grapes evenly over the top and return it to the oven.
Immediately lower the oven temperature to 180°C/160°C fan and continue to bake for 35-40 minutes, or until a skewer inserted into the centre of the cake comes out clean.
Remove the cake from the oven and set it aside to cool in the tin for 30 minutes before removing it from the tin.
The cake can either be served straight away or stored in an airtight container.
I served it as a dessert with whipped cream spiked with a dash of muscadel wine (brandy will also be suitable)