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Amish Oatmeal Rhubarb Bars

Amish oatmeal rhubarb bars with thick rhubarb filling sandwiched between buttery oat crust layers. A golden crumble top and a spoonable center make these traditional rhubarb crumble bars easy to slice after cooling.
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Prep Time 20 minutes
Cook Time 40 minutes
cooling 1 hour
Total Time 2 hours
Servings: 16 servings
Course: Dessert
Cuisine: American
Ingredients Equipment Method Notes

Ingredients
  

For crust and topping
  • 2 cup all-purpose flour
  • 2 cup old-fashioned oats
  • 1.5 cup brown sugar
  • 1 tsp baking soda
  • 0.5 tsp salt
  • 1 cup butter, melted
For filling
  • 4 cup fresh rhubarb, diced
  • 1.5 cup sugar
  • 0.25 cup cornstarch
  • 1 cup water
  • 1 tsp vanilla extract

Equipment

  • 1 sheet pan

Method
 

Prepare and layer crust
  1. Preheat the oven to 350°F and grease a 9x13-inch baking pan to prevent sticking (aim for a thin, even coating).
  2. Combine all-purpose flour, old-fashioned oats, brown sugar, baking soda, and salt, then stir in melted butter until the mixture looks crumbly and holds together when pressed.
  3. Press half of the oat mixture into the bottom of the prepared pan, using steady pressure to form an even base with no big gaps.
Cook rhubarb filling
  1. Combine fresh rhubarb, sugar, cornstarch, water, and vanilla extract in a saucepan, then cook over medium heat until thickened, about 10 minutes, stirring as it turns glossy and spoon-coating.
  2. Spread the thickened rhubarb filling over the crust in an even layer so the bars bake uniformly.
  3. Sprinkle the remaining oat mixture over the rhubarb filling to create a crumble top, covering most of the surface.
Bake and cool
  1. Bake at 350°F for 35-40 minutes until golden brown, with bubbling around the edges and a set-looking center.
  2. Cool completely before cutting into bars so the filling fully sets into thick layers for clean slices.

Notes

Pro tip: For the cleanest bars, let the pan cool to room temperature (then slice) so the thick rhubarb filling firms up. Store covered in the refrigerator up to 4 days; freeze bars in a sealed container up to 2 months. If you need a gluten-free option, use a 1:1 gluten-free all-purpose flour blend in place of all-purpose flour.