Preheat your oven to 350 degrees.

Rinse your rhubarb stalks with water, chop up two cups and set aside.

Using a mixer, cream together 2/3 cup dark brown sugar, ½ cup softened butter, 1 egg and 1 cup sour cream.

Next, stir together 2 cups all-purpose flour, 1 t. baking soda and ½ t. salt in separate bowl and add this slowly to the creamed mixture just until it is all incorporated.

Fold in your two cups of chopped rhubarb by hand.

Spread the rhubarb filled batter into a greased 13x9 pan.

In another bowl, combine an additional ½ cup dark brown sugar, 1 cup rolled oats, 1 cup chopped pecans, 1 t. cinnamon and ¼ tsp. grated or ground nutmeg.

With a pastry blender, cut in ½ cup of cold butter until you have a crumble.

Spread the crumble on top of the batter and gently press  it down before putting it into the oven.

Bake the cake for 30-35 minutes or until a toothpick comes clean.

Remove the cake and let it cool a bit before slicing.

Serve with real whipped cream.