Pour the wine into a small pan. Bring to
the boil, then keep simmering until reduced
down to 85ml – this will take 5-10 mins.
Leave to cool.
Heat oven to 180C/fan 160C/gas 4. Brush
a 23cm springform cake tin with olive oil,
tip in 1 tbsp flour, then shake all over the
pan until covered. Discard any excess. Beat
together the sugar and butter until creamy
and well combined. Add the eggs, one at
a time, then stir through the zests. Stir
together the cooled wine and olive oil, then
pour a little into the cake mix. Stir, then fold
in a third of the flour and the baking powder.
Keep alternating between adding the liquid
and flour until everything has been incorporated
and the batter is smooth.
Spoon the cake batter into the prepared
tin, then smooth the surface with the back of
the spoon. Scatter the halved grapes over the
top, then sprinkle over the sugar. Bake for
35-40 mins until a skewer inserted into the
middle of the cake comes out clean. Eat
warm or cool. Will store in an airtight
container for up to 3 days.