Rhubarb Custard Bars

Preparation

1. Step 1

   Heat oven to 325 degrees and line a 9-by-9-inch pan with parchment paper, leaving two edges long so they overhang the pan by at least 1 inch. (This is for lifting the bars out later.)

2. Step 2

   In a food processor, pulse together flour, sugar and salt. Add butter and process until a crumbly dough forms. Press dough into the lined pan in an even layer. Don’t clean out the food processor, you’re going to need it.

3. Step 3

   Bake crust until golden at the edges, 35 to 40 minutes, rotating halfway through. Transfer to a wire rack and raise oven temperature to 350 degrees.

4. Step 4

   While the crust is baking, make the filling. In a medium saucepan, combine the rhubarb slices and 1 cup sugar. Cook, stirring frequently, over medium-low heat until rhubarb releases its juices. Raise heat and bring to a simmer. Keep simmering, stirring once in a while, until the rhubarb breaks down completely, about 15 to 20 minutes. Transfer the rhubarb and juices to the food processor, and let it sit with the cover off until it cools down a bit, about 15 minutes.

5. Step 5

   Meanwhile, using a vegetable peeler, lay the very pink rhubarb stalk on its narrower side. From the edge of the stalk, peel a long strip from the stalk. Continue to peel strips from the stalk, flipping it around the other side to keep it even. (This makes it easier to peel, but don’t worry too much about getting uniform strips.) Line up peeled strips and cut into 1½-inch lengths. Some may curl up, and that’s fine. You’ll have about 1 cup strips.

6. Step 6

   To the food processor, add the eggs, remaining ¼ cup sugar, lemon juice, flour, zest and salt, and pulse until mixture is puréed. Pour into baked shortbread base, and carefully scatter the rhubarb strips on top. It should look a little like confetti. Bake until the filling is set and puffy, 20 to 30 minutes. Transfer to a wire rack to cool completely in the pan.

7. Step 7

   Once cool, use a butter knife to cut at the edges of the crust to release them from the pan, then use the parchment “handles” to lift up and transfer the pastry to a cutting board. Cut into 1¾-inch squares. Dust with confectioners’ sugar before serving.