Preheat oven to 350.

Rub butter on bottom an 8x8 baking dish.

Place plums in baking dish and sprinkle with sugar. Stir to mix.

In a separate bowl, stir together flour, brown sugar, oats, cinnamon and salt.

Using a fork or a pastry cutter, work butter into mixture until it is well combined and crumbly.

Sprinkle mixture over plums.

Bake at 350 for 35-45 min.