Preheat oven to 400° F and line an 8x8 baking dish with parchment paper.

In a large bowl, stir the flour, sugar, baking powder, and salt together. Then, use a cheese grater to grate the cold butter directly into the bowl.

Use your hands to combine until the butter resembles small pebbles. Last, add in the egg and milk and stir to combine.

In a separate medium bowl, add the plums, along with the sugar, flour and vanilla and stir to combine.

Add ⅔ of the crust mixture to the prepared baking pan, using your hands to press it down.

Scoop the plum mixture into the pan, spreading it into an even layer. Then, sprinkle the remaining crust mixture over top.

Place the pan in the oven and bake the bars for 30-32 minutes until the edges are golden brown. Remove from the oven and allow the bars to cool at room temperature. Slice and enjoy!