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1
Make the jam: Combine rhubarb, sugar, and 1/2 cup water in a medium saucepan.
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2
Split vanilla bean, scrape the seeds into the pan, and toss in the pod.
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3
Bring to a simmer over low heat, cook, stirring often, until rhubarb softens and forms a soft mass, about 10 minutes.
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4
Remove and discard vanilla bean.
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5
Transfer to a shallow bowl and let cool.
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6
Can be made ahead and refrigerated in an airtight container, for up to one week.
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7
If refrigerated, return to room temperature before using.
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8
You may substitute 1 cup of your favorite jam or preserves for the homemade.
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9
Make the shortbread: In a medium bowl, whisk together flour, baking powder, and salt.
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10
In the bowl of an electric mixer fitted with the paddle attachment, beat butter on high speed until pale and fluffy.
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11
Add egg yolks and sugar, and beat until sugar is dissolved and the mixture is light.
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12
Reduce mixer speed to low, and add the dry ingredients, mixing only until the ingredients are incorporated.
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13
Turn the dough out onto a work surface and cut into two pieces.
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14
Shape each piece into a ball and wrap in plastic wrap.
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15
Place in freezer until firm, about 30 minutes.
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16
Can be made ahead and frozen for up to one month.
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17
Thaw in refrigerator overnight.
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18
Assemble and bake: Preheat oven to 350u00b0 with rack in center.
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19
Remove one ball of dough from freezer and, using the large holes on a box grater, grate the dough into a 9-by-13-inch baking dish.
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20
Pat the dough gently just to get it into the corners (you don't want to press it down), and spread with the rhubarb jam.
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21
Grate the remaining dough over the jam, and press it lightly to distribute it evenly.
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22
Bake until golden brown, about 40 minutes.
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23
Dust with confectioners' sugar as soon as it is removed from oven.
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24
Cool on a wire rack.
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25
Cut the shortbread into bars when it is cool.
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26
You can cut whatever size bars please you, although as a rough guide, 3-inch squares, or rectangles 1 1/2 inches by 3 inches make nice servings.
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27
Store covered at room temperature for up to 2 days.
