In the bowl of an electric mixer, using the paddle attachment, combine butter, flour, salt and sugar on low speed until it resembles fine crumbs. (You can also use a wooden spoon or just your hands if you prefer not to use a mixer)

Add the water to the crumbly mixture and mix on low just until the dough comes together.

Remove from the bowl and wrap in plastic wrap, forming a round disc.

Place in the refrigerator and chill for about 2 hours.

Preheat oven to 400 degrees.

Combine sugar and cinnamon and set aside.

Roll out chilled dough on a lightly floured surface to about 1/8th of an inch. Transfer to tart pan with removable bottom, trimming edges, and pricking the bottom of the tart all over with a fork.

Sprinkle the breadcrumbs over prepared crust evenly. (Bread crumbs help to protect the shell from moisture of the plums as they cook, allowing it to stay crisp.

If plums are small cut them in half, otherwise cut into quarters or even into 8ths depending on their size. Make a small slit at the end of each plum slice.

Arrange plums over breadcrumbs covering the entire surface.

Bake for 35 to 40 minutes, until fruit is tender and tart is nicely golden.

Remove from oven and sprinkle with the cinnamon and sugar.

Allow to cool slightly before serving.