Lovely roasted rhubarb and strawberry filling, folded inside a flaky buttermilk biscuit.
Preheat oven to 350F.
In a large bowl, toss the prepared rhubarb and strawberries with 1/3 cup white sugar and the vanilla. Spread in a single layer onto a baking sheet. Bake stirring 2-3 times, until juices have thickened but are not beginning to brown, about 45-50 minutes (may take longer if starting with frozen rhubarb). You should have about 1 cup of roasted fruit. Immediately remove roasted fruit to a bowl and allow to cool completely before proceeding and ideally, cover and pop the bowl of fruit in the fridge for a bit, so it will be cold when using. *Roasted fruit can be made several days ahead and refrigerated.
Increase oven temperature to 400F. Prepare a baking pan with a sheet of parchment paper. Set aside.
Be sure to read the "Cook's Notes" included with this post, where I share some valuable tips, options, substitutions and variations for this recipe!