1 stick (4 ounces) unsalted butter, cut into 1/2-inch dice
Preheat the oven to 375°. In a shallow 2-quart baking dish, toss together the first five ingredients.
In a bowl, mix the flour with the brown sugar, almonds and salt. Cut or rub in the butter until the mixture resembles coarse meal. Sprinkle the topping over the plums and set the dish on a baking sheet. Bake for about 45 minutes, or until the topping is lightly browned and the fruit is bubbling.