I know it's a little late in the season but here it is anyway . . .
2 lbs rhubarb, cut into 1" pieces
1-1/4 cups white sugar
1/4 cup all purpose flour
1 tsp vanilla extract
1/4 tsp ground cardamom
1 cup all purpose flour
1/2 tsp salt
1 cup light brown sugar
1/2 cup of butter, cut into cubes
Preheat oven to 375F. In a medium sized bowl, mix together the rhubarb, white sugar, 1/4 cup of flour, the vanilla extract, and the ground cardamom. Spoon into a 9 x 13" baking dish.
In a food processor, pulse together 1 cup of flour, the salt, and the brown sugar. Add the butter and pulse until the pieces of butter are pea-sized. Spread topping mixture over rhubarb mixture.
Place in oven and cook for 35-45 minutes, until the filling is bubbly and the topping is lightly browned. Let cool for at least a half an hour before serving.
Serve with vanilla ice cream or whipped cream.