Strawberry-Rhubarb Oatmeal Bars

Depeding on the tartness of the rhubarb, and the sweetness and juiciness of the strawberries, I sometimes adjust the sugar and/or cornstarch a bit with this recipe...

Ingredients, oatmeal base:
1 C butter
2 C brown sugar
2 eggs 
½ tsp vanilla
3 C oats
2½ C flour
1 tsp baking soda
1 tsp salt

Ingredients, strawberry-rhubarb layer:
3 C rhubarb, large diced (1")
3 C strawberries, large diced
¾ C sugar
zest of one orange (approx 2 tsp zest)
1/3 C orange juice
2 T cornstarch

Crumble Topping Ingredients
¾ C flour
1 C rolled oats
¼ C sugar
½ C brown sugar
½  tsp salt
¾ C butter, diced

Directions:
Preheat oven to 350˚.

To make oatmeal base...
Cream together butter and brown sugar; beat in eggs and vanilla until smooth. Stir in oats. Add flour, soda and salt all at once, stirring until well combined. Spread evenly over a jelly roll baking sheet, and just slightly up the edge (baking sheet with a 'lip'). Bake 12 minutes; remove and cool slightly while you prepare filling and topping.

To make the fruit filling...
In a large bowl, combine rhubarb, strawberries, sugar and zest. Dissolve cornstarch in orange juice; add to rhubarb-strawberry mixture and gently stir to combine. Spoon or pour mixture over oatmeal base.

In a large bowl, stir together first 5 ingredients of crumble topping to evenly distribute. Cut in butter and continue mixing until mixture resembles coarse crumbs. Sprinkle generously over strawberry-rhubarb layer. Bake 30-40 minutes until fruit is bubbling and crumble topping is golden brown.

Cool completely. Slice into bars to serve.