put rhubarb in greased pie plate or 9" x 9" pan. Mix flour, 1 cup sugar, salt, and cardamom. Sprinkle evenly over the fruit over the fruit.
In food processor, combine 3/4 c. flour with brown sugar, powdered sugar, and butter. Pulse til crumbly. Last, add oatmeal and pulse only a time or two so oats are mixed in but don't get chopped too fine.
Sprinkle crumble topping over fruit patting down very lightly.
Bake 40-45 minutes in 350 degree oven. Serve warm or cold with whipped cream or ice cream if desired. Enjoy!