Grease an 850ml pudding basin with oil and line with 2 sheets of clingfilm, letting a little bit overhang.
Remove any stalks from the berries. Hull and quarter the strawberries (if using).
Place all the berries in a large, heavy-based saucepan with the sugar, orange juice and vanilla paste (if using).
Cook over a low heat for 3 to 5 minutes, or until the sugar dissolves and juices start bleeding from the fruit. Set aside to cool.
Remove the crusts from the bread, then spread over the jam.
Line the basin with 6 of the slices, jam-side up. Overlap slightly to ensure no gaps, and press the bread against the sides.
Spoon the cooled fruit and half its juice into the lined basin, reserving the remaining juice.
Cover the pudding with the last slice of bread, jam-side down, then pull over the overhanging clingfilm.
Place a saucer that fits inside the basin on top of the pudding, then place a weight, about 2kg, on top of it. Refrigerate overnight to soak up the juices.
Strain the leftover juice through a fine sieve into a small pan. Bring to the boil, then simmer for 5 to 10 minutes, or until the juice has reduced into a light syrup. Pour into a jug and keep in the fridge.
To serve, open the clingfilm and carefully invert the pudding onto a plate.
Drizzle large slices with the syrup and serve with crème fraîche or cream, if you like.