Adapted from Smitten Kitchen
2 cup rolled oats
1 ½ cup plus up to 2 tablespoons flour
1 cup light brown sugar
½ tsp table salt
12 Tbsp unsalted butter, melted
2 tsp cornstarch
2 Tbsp lemon juice
2 Tbsp granulated sugar, divided
2 cups diced rhubarb- bright red stalks!
2 cups diced strawberries
Heat oven to 375°F. Line bottom of pan with parchment paper or coat with butter.
Add oats, 1 ½ cup flour, brown sugar, and salt directly into the baking pan and mix. Pour in melted butter and stir to form clumps. Add remaining 2 T flour if clumps feel too soft. Remove ½ cup of the mixture, set aside. Press remaining mixture into the bottom of the baking pan to form an even crust.
Spread half the rhubarb & strawberries over the crust. Sprinkle the fruit with cornstarch, lemon juice, and 1 tablespoon of granulated sugar. Distribute the remaining fruit on top, and sprinkle with second 1 tablespoon sugar. Scatter reserved ½ cup of crumb mixture over fruit and bake bars for 40 minutes-50 minutes, until fruit is bubbly and the topping is golden brown.
Let cool in pan.