Mix ingredients for bottom layer in a large bowl and allow to
stand several hours, stirring once or twice.
Preheat oven to 350F.
Whisk dry topping ingredients in another bowl, leaving a well in
the center. Melt butter and pour into dry ingredients; mix until
combined.
Pour rhubarb and juice into a buttered 9” x 13” glass pan.
Crumble the topping over the top evenly without compressing. Bake
for 50 minutes to one hour, until gently browned.
Serve hot or cold, with creme fraiche, yogurt or ice cream.