Ingredients
Equipment
Method
Prep the pan and make the oat crumble
- Preheat the oven to 350°F and grease a 9x13-inch baking pan, so the bars release cleanly later.
- Combine all-purpose flour, old-fashioned oats, brown sugar, baking soda, and salt, then stir until evenly mixed.
- Pour in the melted butter and stir until the mixture turns into an even, crumbly texture with no dry pockets.
- Press half of the oat mixture into the bottom of the prepared pan to form a firm crust layer.
Cook and layer the rhubarb filling
- In a saucepan, combine fresh rhubarb, sugar, cornstarch, water, and vanilla extract.
- Cook over medium heat for about 10 minutes, stirring until the mixture thickens and looks glossy.
- Spread the thickened rhubarb filling over the crust in an even layer.
- Sprinkle the remaining oat mixture on top to fully cover the filling for a crumble finish.
Bake and cool
- Bake at 350°F for 35-40 minutes, until the top is golden brown and the center looks set.
- Cool completely before cutting into bars, so the filling firms up and the layers hold their shape.
Notes
Pro tip: cool the pan fully (about 1 hour) before slicing so the rhubarb filling thickens enough for neat bar layers. Store covered in the refrigerator up to 4 days; freeze baked bars up to 2 months (thaw overnight in the fridge) for best texture. For a lighter option, you can reduce sugar slightly in the filling, but expect a softer set.