In a mixing bowl, beat together the softened cream cheese, butter, and 1 cup of sugar until smooth. Add in the egg and vanilla extract, mixing until fully combined.
In another bowl, combine the flour, baking powder, and salt. Gradually add this dry mixture to the cream cheese mixture, blending well.
Spread the batter into a greased baking dish and top with chopped rhubarb. Sprinkle the remaining sugar over the rhubarb.
Bake for 30 minutes or until the top is golden and set.
Let cool before cutting into bars.
Notes
For a sweeter filling, increase the sugar in the filling mixture.