Make a sugar syrup by dissolving 200 g sugar in 120 ml water over a gently heat. Slice 3 blood oranges into
3 mm slices and put into the syrup, bring back to a simmer and cook gently for about 15 minutes. Let cool.
Grease and flour a 23 cm diameter deep cake tin, and line the bottom with a disk of baking parchment. Layer
the orange slices in the bottom of the tin, starting with the centre, overlapping slightly, and drizzle a couple
of Tbs of the syrup over the oranges.
Mix 180 g plain flour, 2 tsp baking powder and the grated zest from an orange. In another bowl, cream together
180 g softened butter with 180 g caster sugar, until light and fluffy, then add 3 eggs, one at a time, beating
each one until well mixed. Fold in the flour mixture until just combined, then stir in 4 Tbs milk. Pour into
the tin over the oranges, smooth the top and bake in a 180°C oven for about 40 minutes, until golden on top and
a knife poked into the centre comes out clean. Let the cake cool in the tin for 5 minutes, then run a knife
around the edge and invert onto a cooling rack. Peel off the baking paper, and drizzle over a couple more Tbs
of syrup. Serve with a dollop of mascarpone and some extra syrup, if desired.