Spread the plums in a buttered 8 inch square or 1 1/2 quart baking dish.
Sprinkle with the brown sugar.
Pour the orange juice over the top.
Combine the baking mix, salt and sugar in a large bowl and stir to mix.
Combine the egg, milk, vegetable oil and vanilla in a separate bowl and blend.
Add the milk mixture to the dry ingredients and stir just until moistened.
Pour over the plum layer.
Bake at 375 degrees for 45 minutes or until golden brown.