Combine rhubarb, 1/2 cup (125 mL) brown sugar and the water in a heavy saucepan set over medium heat. Bring to a boil. Simmer, stirring often, for 10 to 12 minutes or until rhubarb is soft and thickened to an applesauce consistency. Cool to room temperature.
Preheat oven to 325 degrees F (160 degrees C).
Toss cookie crumbs with melted Spreadables butter until well combined. Press into bottom of a parchment paper-lined, 9-inch (23 cm) baking dish.
Whisk sour cream with remaining sugar and flour until well combined; whisk in eggs and vanilla just until smooth. Pour over prepared crust. Dollop rhubarb mixture over top and swirl with a knife until evenly marbled.
Bake for 28 to 30 minutes or until centre is just slightly jiggly. Cool to room temperature, then chill thoroughly before slicing.