Mix together flour, baking powder, and a salt. Add Flour mix alternately with milk & vanilla to butter mix. Chill dough.
On floured board, roll dough ¼ inch thick. Using a 2" cookie cutter, cut out cookies. Place cookies on a greased cookie sheet.
Fill cookies with rhubarb pudding. Cover with another cookie and press edges together. Bake in 400° oven for 10 minutes.
Note: I think a date filling would be excellent in this too.