5stalks rhubarb (each about 14" long and 1" wide, about 1 pound total), cut into 1/2" pieces
3/4cupsugar (or try 1/2 cup agave)
1/2" knob of ginger, finely grated
1/2vanilla bean, split and scraped
zest and juice of 2 blood oranges
3/4cupplus 2 tablespoons whole spelt flour (or use 3/4 cup all-purpose)
1egg plus 1 egg yolk (use 3 eggs if doubling recipe)
1/4cupplus 3 tablespoons flour
Brown the butter:
Place the butter and vanilla bean in a medium saucepan and melt over medium heat. Continue cooking, swirling the pan occasionally, for about 5 more minutes. The butter will foam up a lot, then it will turn a golden-brown and smell nutty and good. Watch closely so that it doesn't go too far; remove from the heat. Measure out 1/4 cup of the browned butter and set aside for the topping. Pour the rest of the butter (1/2 cup) into a small metal bowl and freeze for 30 minutes, for the crust.
Make the jam:
In a medium saucepan, combine the 3/4 cup sugar, grated ginger, vanilla bean pod and scrapings, orange zest and juice. Over high heat, bring the mixture to a simmer, then dump in the rhubarb. Cook, stirring frequently, until the mixture has broken down into a thick jam, about 10 minutes. Set aside to cool, and remove the vanilla bean. (You can wash it, leave it to dry at room temp, and reuse.) Measure out 1 1/4 cups of jam, and save the rest to enjoy on toast or otherwise.
Make the crust:
Sift the 3/4 cup plus 2 tablespoons flour, powdered sugar and salt into a bowl. Cut the frozen butter into tiny chunks and add to the flour mixture, working with a pastry blender or your fingers until large clumps of dough start to cling together and most of the butter chunks are gone. (You could also use a food processor for this.) Line an 8x8" square pan with a sling of parchment paper, and press the crust mixture evenly into the bottom. Chill the pan for 30 minutes.
Make the topping and bake the squares:
Position a rack in the center of the oven and preheat to 375º.
Bake the crust until golden and firm, 15 - 20 minutes. Remove and let cool.
In a medium bowl, whisk together the eggs, brown sugar, flour and salt to combine. Re-melt the 1/4 cup of brown butter and gradually whisk it into the topping to create an emulsion. Spread half of the brown butter topping over the cooled crust. Dollop 3/4 of the jam over the brown butter topping, spreading slightly, then spread the remaining brown butter topping over the jam. Drop the remaining jam onto the bars in random dollops. Return the bars to the oven and bake for 30 - 35 minutes, until the topping is firm and golden. Let cool completely, then cut into 12 bars.
These bars are sturdy enough to travel well, but are best eaten within the first couple of days, when the crust is still crisp. They'll keep for up to a week, but store them in the fridge after a day or two.