Heat oven to 190C/fan 170C/gas 5 and butter a non-stick 23cm ring tin. Arrange the peaches, cut side up, in the base if the tin, then randomly spoon in the peach conserve and scatter over the redcurrants.
To make the cake, beat together the flour, baking powder, butter, sugar, eggs, vanilla and milk until well mixed, then stir in the sour cream. Spoon the mixture into the cake tin, then level the surface.
Bake for 35-40 mins until the cake is well risen, golden, and springs back when lightly pressed. Cool for a few mins, then carefully turn out onto a plate. You can serve warm with cream as a dessert or cold as a cake.