In a medium saucepan over medium-high heat, combine the rhubarb, granulated sugar, and vanilla bean and bring to a boil. Reduce heat to low. Cover and simmer until the rhubarb is barely tender, about 5 to 6 minutes. Stir in the strawberries, remove from heat, and let cool. Remove the vanilla bean.
Whip the cream with the confectioners' sugar until soft peaks form. To serve, top each slice of cake with some warm conserve and a few dollops of whipped cream.