To make the topping, combine the flour, oats, and brown sugar, and stir to combine.
1 ½ cups old-fashioned oats, 1 cup all-purpose flour, 1 cup brown sugar
Add the butter and vanilla, and cut in until the mixture looks crumbly.
½ cup cold butter, ½ teaspoon vanilla extract
Crumble the topping over the filling.
Bake in the preheated oven until the filling is hot and bubbly all the way through and the topping looks crispy and light golden brown, about 45-50 minutes.
Notes
Rhubarb: You can use an equal amount of fresh rhubarb.
Sugar: Feel free to adjust the amount of sugar in the filling depending on how sweet and ripe your strawberries are and how sweet you'd like the filling to be.
Brown sugar: Light brown sugar or dark brown sugar will work.
Butter: I use salted butter. If you're using unsalted butter, add a pinch or two of salt.