Ingredients
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2 cups plus 2 tbsp all-purpose flour, divided
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1 1/2 sticks (3/4 cup) plus 2 tbsp unsalted butter, divided
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3/4 cup confectioners' sugar, plus more for dusting
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3 cups chopped rhubarb pieces (2" pieces)
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1 3/4 cups granulated sugar
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2 lemons
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3 large eggs, separated
Steps
1
Preheat oven to 350°F. In a medium bowl, combine 2 cups flour, 1½ sticks butter, and confectioners’ sugar. Cut butter into dry ingredients with two butter knives or a pastry knife. Mix until a crumbly texture. Press crumb mixture into a 10x15" jelly roll pan. Bake 10 minutes. Remove pan from oven and increase oven to 375°F.
2
Meanwhile, in a medium pot on medium, combine rhubarb and granulated sugar. Cook 13 to 14 minutes, until rhubarb is soft but still holds its shape. If desired, purée rhubarb with a handheld immersion blender. Let cool.
3
Melt remaining 2 tablespoons butter in microwave-safe bowl. In a medium bowl, combine melted butter, juice of both lemons, remaining 2 tablespoons flour and egg yolks. Stir in cooled rhubarb mixture.
4
Using a stand mixer or hand mixer, beat egg whites on high 1 to 2 minutes, until foamy. Beat egg whites into rhubarb mixture until just combined. Spread mixture onto crust. Bake until set, 30 to 35 minutes. Let cool completely. Dust with confectioner’s sugar. With a paring knife, cut tray into 9 rows. Cut each row into 1" squares.
