A tangy, gooey filling that tops off a buttery almond shortbread – whoa. Borrowed from, ‘The Harvest Baker’, by Ken Haedrich, you should be making these right now!
1/2 c. whole almonds AND 1/4 c. sugar AND 1/4 t. salt
1 c. flour AND 1/2 c. cold butter, cut into cubes
2 c. diced rhubarb AND a bit of butter for baking
1 1/3 c. brown sugar AND 1 1/2 T. flour AND a pinch of salt
5 T. butter, melted but barely warm AND 4 t. vinegar AND 1 t. vanilla
Preheat the oven to 350, butter a 9 x 9 cake pan, line it with parchment (so that you have handles to help you to remove the squares), and butter the parchment.
For the bottom – add the almonds, sugar and salt to your food processor and process until the almonds are finely ground. Add the flour and pulse to mix, then scatter in the butter cubes and pulse again until the mix is crumbly but starting to come together. Scrape the mix into the bottom of your prepared pan, spread it around evenly and then use the back of a measuring cup to firmly press it all in. Place the pan in the freezer for 15 minutes (this is a good moment to roast the rhubarb), then bake the crust for 15 minutes before removing it from the oven to a rack to cool.
For the filling – lightly butter a parchment-lined baking sheet, spread out the diced rhubarb and roll it around to coat it. Bake for 12 minutes and then remove the rhubarb from the oven to a rack to cool.
In a large bowl, whisk together the brown sugar, flour and pinch of salt, then crack in the eggs and thoroughly whisk to combine. Whisk in the melted butter, vinegar and vanilla and then stir in the cooled rhubarb. Pour the filling over the cooled crust and do your best to spread the rhubarb pieces around evenly. Bake for 35 to 40 minutes until the middle no longer wiggles and the edges are browned and crusty.
Leave the squares to cool completely in the pan, then use a straight edge to carefully loosen all of the edges before lifting the squares out onto a cutting board to divide. Squares that have been refrigerated probably cut the smoothest, but no one will complain about how perfect the squares are – enjoy!