Refreshingly tart rhubarb enveloped in a sweet lemony custard layer with a buttery shortbread base. Topped with toasted Swiss meringue, these bars are an excellent way to highlight the vibrant pink color and unique flavor of rhubarb as it makes its all-too-brief appearance in spring.
½cup (113g, 4oz)cold unsalted butter, cut into cubes
¼cup (50g)granulated sugar
1cup (120g)all-purpose flour
¼teaspoonkosher salt
LEMON RHUBARB CUSTARD LAYER
3Tbsp (23g)all purpose flour
¾cup (150g)granulated sugar
2largeeggs, beaten
¼cup (60mL)heavy whipping cream
zest of 1 lemon
¼cup (60mL)lemon juice, freshly squeezed (approx. 1 large lemon)
½teaspoonlemon oil or extract
3cups (366g, 0.8lb)rhubarb, diced
SWISS MERINGUE TOPPING
3egg whites (approx 100g)
¾cup (150g)granulated sugar
¼teaspoonvanilla extract
Instructions
SHORTBREAD LAYER
Preheat the oven to 350° F (177 C, gas mark 4).
Line an 8" (20 cm) square pan with parchment paper, extending a flap of parchment over opposite sides as a handle to aid in removing the bars later.
In the bowl of a stand mixer fitted with the paddle attachment, combine the butter, sugar, flour, and salt and mix until the dough begins to come together with a lumpy, sandy texture.
Dump the dough into the prepared pan and press with your fingers until it is spread evenly into all areas of the pan. Cover with plastic wrap and use the flat base of a drinking glass or the bottom of a measuring cup to smooth the top and firmly pack down the dough. Chill in the fridge for 30 minutes.
Bake the shortbread for 10-12 minutes, until top has gone from shiny to dull, shortbread is just baked through, barely starting to turn golden brown, and beginning to smell like toasted butter. Remove from oven and set aside to cool on a baking rack.
LEMON RHUBARB CUSTARD LAYER
In a medium size bowl, whisk together flour and sugar. Add eggs and whisk to combine. Add cream, lemon juice, lemon zest and lemon extract and mix until completely blended. With a spatula, fold in chopped rhubarb and pour custard mix onto cooled shortbread crust. Rap pan firmly on countertop several times to remove air bubbles that may have formed in custard.
Bake at 350° F (177C, gas mark 4) for 40-45 minutes, until custard layer is completely set - it should not jiggle. Cool completely on a rack. Once cool, place in refrigerator to set for at least one hour.
SWISS MERINGUE TOPPING
In a small (1 qt ) saucepan, whisk together egg whites and sugar. Heat over low heat, whisking frequently, until mixture is warm and granulated sugar has dissolved. Rub some of the egg white mixture between your fingers (carefully - it might be hot). If you feel sugar granules, keep mixing until it feels smooth. If you have a thermometer, it should read 160° F (177 C).
Transfer warm egg mixture to the bowl of a stand mixer fitted with the whisk attachment. Beat until stiff peaks forms and mixture has a glossy sheen - about 5 minutes. The meringue should be very thick and hold its shape (no drooping) when the whisk is dipped into the mixture and turned upright.
To top the bars, you can either spread a full layer of meringue onto the top, or opt to pipe meringue decorations on each bar as I did. Remove fully chilled bars from pan. Place bars onto a metal baking sheet, removing the parchment paper from underneath (kitchen torches and paper do not mix!)
To spread meringue over the bars: Scoop the meringue out onto the baked custard and gently spread evenly to cover the filling, making swirls with an offset spatula or spoon. Toast the meringue using a kitchen torch. Slice into 16 squares, wiping the knife clean in between each cut.
To pipe meringue onto the bars: Slice into 16 squares, wiping the knife clean in between each cut. Prepare a 16" (40cm) piping bag with a decorative tip. A St. Honore tip would be ideal for the zig zag pattern that I piped. I didn't have one and ended up using an Ateco 366 leaf tip with the "beak" held sideways, perpendicular to the bars. Be creative with the piping - most large or jumbo tips with a wide enough opening will work well for meringue. Toast the meringue using a kitchen torch.
Serve immediately. Keep extra bars refrigerated in a single layer in an airtight container.