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Amish Oatmeal Rhubarb Bars

Amish oatmeal rhubarb bars with thick rhubarb filling sandwiched between buttery golden oat layers. Bake a crumbly oat crust, spoon in a lightly thickened rhubarb mixture, and finish with a top layer of oats for classic crumble-bar texture.
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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
Calories: 320
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
 

Prep and make the oat crumb
  1. Preheat the oven to 350°F and grease a 9x13-inch baking pan.
  2. In a large bowl, combine all-purpose flour, old-fashioned oats, brown sugar, baking soda, and salt, then stir until evenly mixed.
  3. Pour in the melted butter and stir until the mixture forms a crumbly texture.
  4. Press half of the oat mixture into the bottom of the prepared pan to form an even crust layer.
Cook the rhubarb filling
  1. In a saucepan, combine diced rhubarb, sugar, cornstarch, water, and vanilla extract.
  2. Cook over medium heat for about 10 minutes, stirring, until the mixture thickens into a filling consistency.
  3. Spread the rhubarb filling over the pressed crust layer.
  4. Sprinkle the remaining oat mixture evenly over the top to cover the filling.
Bake and cool
  1. Bake at 350°F for 35-40 minutes, until the top is golden brown.
  2. Cool completely in the pan for 1 hour before cutting into bars, so the filling sets cleanly.

Notes

For thick, scoopable bars, let the pan cool fully at room temperature (1 hour) before cutting. Store covered in the refrigerator for up to 4 days; freeze bars in an airtight container for up to 2 months. For a lighter option, substitute half the brown sugar with light brown sugar or a 1:1 sugar alternative to reduce overall sweetness without changing the crumb structure.