Grease 12 mini brioche moulds, each with a capacity of 40–50 ml (1¾–2 fl oz).
Beat together the butter and caster sugar until light and fluffy. Gradually beat in the egg and vanilla extract, adding a little flour to prevent the mixture curdling. Sift the flour and baking powder into the bowl and stir in gently. Divide among the moulds and level the surfaces.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes until just firm to the touch. Leave for 5 minutes, then transfer to a wire rack to cool.
Make the topping by putting the redcurrant jelly in a small saucepan with the measurement water and heating gently until the jelly has dissolved. Turn into a small dish. Whip the cream with the icing sugar and rosewater until just holding its shape. Spoon on top of the shortcakes and decorate with strawberry halves. Drizzle with the redcurrant syrup.