Step 1

Preheat the oven to 350 F. Grease a 9 by 13 pan.

Step 2

In a large pot, add the diced rhubarb, water, sugar, and lemon juice. Bring to a boil then reduce heat to a simmer. Cook until the rhubarb has softened, about 20 minutes. Turn off the heat and stir in the vanilla. Let cool a few minutes. After the rhubarb has cooled slightly, carefully transfer the mixture to a blender. Blend until smooth. Set aside until needed.

Step 3

In a large mixing bowl, add the flour, rolled oats, brown sugar, cinnamon, baking soda, salt, nutmeg. Stir. Add in the soften butter and mix until fully incorporated and the mixture resembles coarse crumbs. Reserve 1 cup of the mixture for the topping.

Step 4

Add the remaining mixture to the greased baking pan and pat down the mixture into an even level.

Step 5

Pour the rhubarb filling on top of the crust and spread it evenly. Crumble the reserved crust mixture on top of the filling.

Step 6

Bake 35-40 minutes, or until the filling has set. The bars will continue to firm up as they cool.

Step 7

Let the bars cool completely before cutting.