Preheat the oven to 180oC/350oF/Gas
4. Using greaseproof paper, line a 25 x 5cm tin and grease the paper.
For the topping, combine the flour, light brown sugar and cinnamon in a
bowl. Add the butter and rub in until it resembles coarse breadcrumbs.
Cream the butter or margarine and
sugar until light and fluffy. Beat in the eggs, one at a time. Stir in
the vanilla. In three batches, sift, then fold in the flour and baking
powder.
Pour the mixture into the tin. Arrange
the plums on top and sprinkle with the topping.
Bake until a skewer inserted in the
centre comes out clean, about 45 minutes. Cool in the tin.
To serve, run a knife around the
inside edge and invert on to a plate. Invert again on to a serving plate
so the topping is uppermost.