3 cups flour
1/2 cup sugar
1/2 cup brown sugar
1 tsp. baking powder
1/2 tsp. cinnamon
14 tsp. salt
1 cup butter, cold and cubed
1 egg
2 tsp. vanilla
1/4 cup milk
1/3 cup old fashioned oats (not quick)
Filling:
2 1/2 cups chopped strawberries
2 1/2 cups sliced rhubarb
1/2 cup sugar
1 Tbsp. cornstarch
1 tsp. orange zest
For the crust and topping, whisk together the flour, sugar, brown sugar, baking powder, cinnamon, and salt together in a large bowl. Add the cubed butter and use a pastry cutter, two forks, or your fingers, to cut in the butter until the mixture resembles coarse crumbs. (You can also do this step in a food processor; just pulse a few times til you get the coarse crumbs - don't just turn "on" or it won't be crumbly anymore!)
In a small bowl, whisk together the egg, milk, and vanilla. Pour over the flour mixture and use a spoon or your hands to combine. Set aside 2 cups of this mixture.
Press the remaining dough into a greased 9x13 pan. (If you really like parchment paper, you can make a parchment "liner" instead.) You will probably need to use your fingers to flatten it.
For the filling, mix together the strawberries, rhubarb, sugar, cornstarch, and orange zest. Spread over the crust. Sprinkle the remaining 2 cups of flour mixture over the filling. Then sprinkle the oats on top and use a spatula to gently press the topping down.
Bake at 350 for 44-50 minutes until the top is lightly browned and a toothpick comes out mostly clean (it will have some fruit specks, likely). Allow the bars to cool on a wire rack, or place them in the fridge after an hour of cooling to cool them faster.
Cut into squares and serve!
These bars store best in the fridge, and can also be frozen for up to three months. I like to "warm" them up in the microwave or toaster oven if they've been cold, and then top with vanilla ice cream!