1/2teaspooncoarse kosher salt, or 1/4 tsp fine salt
1/2teaspoonground cinnamon
3/4cupunsalted butter, melted
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Instructions
In a medium saucepan, stir together the rhubarb, strawberries, lemon juice, white sugar and cornstarch. Heat over medium heat on the stove-top, stirring regularly. When the fruit softens sufficiently, use a potato masher to break it up into smaller pieces. Continue cooking until mixture comes to a boil and thickens, then remove from heat. Stir in vanilla. Allow mixture to cool to lukewarm before proceeding (or can be made ahead and refrigerated. Bring back to room temperature before proceeding).
Heat oven to 350F degrees (not fan-assisted) and line an 8 x 8-inch pan with parchment paper with overhang on all sides.
In a large bowl, combine oats, flour, whole wheat flour, brown sugar, baking powder, salt and cinnamon. Add melted butter and stir until the mixture forms streusel-like crumbs.
Press 2/3 of the crumb mixture into an even layer at the bottom of the prepared pan. Spread the cooled strawberry rhubarb filling in an even layer over the crust, then sprinkle the remaining crumb mixture evenly over the top of jam.
Bake until jam bubbles at edges and streusel is lightly browned, 30 to 35 minutes. Cool completely before slicing into 12 pieces. (*I like to cool to room temperature and then refrigerate a bit before slicing. It just makes for a neater slicing if you'd like to serve it as neat squares).
Notes
Be sure to read the notes above this Recipe Card, where I share some valuable tips, options, substitutions and variations for this recipe!