Grease a pie pan with non-stick spray.

Make the dough: Mix the flour and baking powder in a small bowl and set aside. 

In a stand mixer fitted with a paddle attachment, cream the butter and sugar until it is light, fluffy, and smooth, about 5 minutes. Add in the egg and vanilla, and mix until well combined. Gradually add the flour and baking powder and mix until a dough is formed.

Divide the dough into 2 equal portions. Roll out each portion between two sheets of parchment to ¼-inch thick, and refrigerate on a baking sheet for 8-10 minutes, until slightly firm but still malleable.

Assemble: Gently line the bottom of the pan with one piece of dough. Place the plums cut side down in a single layer. Evenly sprinkle the raisin and cinnamon on top of the plums. Gently place the second piece of dough on top of the plum filling. Using your fingertips, gently crimp the dough edges to seal. Refrigerate uncovered for 30 minutes.

Preheat the oven to 350 degrees. Take out the pie, and brush the crust with melted butter and sprinkle the top with sugar. 

Cut a few slits in the crust to let steam escape, and bake for 50-60 minutes until the top crust is golden, the plums are cooked, and the bottom crust is baked. Serve warm or at room temperature.