Grease and line a 9 inch square baking pan, or springform round cake tin
Pre-heat the oven to 350 deg F, 177 deg C Gas Mark 4
Combine the flour, ground almonds, baking powder, cinnamon, nutmeg and salt in a large bowl.
Cream the butter and sugar together until light and fluffy.
Add the egg and vanilla and beat until smooth.
Slowly add the flour mixture and milk and continue to beat until you have a smooth, thick batter.
Pour the batter into the cake tin and smooth the top with a spatula.
Arrange the plum quarters, skin side up, and sprinkle with the extra sugar.
Bake for 60 - 70 minutes until the top is golden and test by inserting a skewer or toothpick,it should come out clean.
While the cake is still hot, run a knife round the edge then set on a wire tray to cool (unless you are serving it hot straight from the pan - your choice!)