Rhubarb Brown Butter Tart

With it being near the end of April and St. George's Day (April 23rd's celebration of England lesser known than St. Patrick's [Ireland], St. David's [Wales], and St. Andrew's [Scotland]) I've started eyeing the rhubarb in my freezer and wondering what to try to make with it besides my usual strawberry rhubarb pie. Seems like a lot of the classic British desserts suggested for St. George's contain rhubarb. So, over the weekend I decided to try baking a rhubarb brown butter tart.

To test the recipe I decided to try halving the recipe and baking it in one of my mini ceramic pie plates from Pottery Barn. While there is always a danger with proportions in baking, I thought the experiment worth trying. The product was edible but I definitely learned some useful lessons. For example the pie filling in this case was a custard. The custard was set by the baking process but very soft and not the chewy texture suggested by the photographs. However, the texture did firm up significantly after refrigerating overnight. I believe that the issue was that my pie plate has a lot of vertical height, in contrast to the tart pan that would probably lose much more moisture during the baking process and have a distinct texture. Next time I cut a tart recipe I will make sure to use a smaller tart pan rather than a pie plate.

I have in mind to try a few other rhubarb recipes including:

Rhubarb buckle 

Rhubarb custard tea cake 

Rustic Rhubarb Honey Almond Tart 

The Recipe:

Makes one 8-9″ tart, 8-10 servings

Almond Press-In Crust:

1/4 cup sliced almonds

1/4 cup powdered sugar, plus extra for sprinkling on the finished tart

1/4 teaspoon fine sea salt

3/4 cup all-purpose flour

6 tablespoons cold, unsalted butter, cut into 1/2″ chunks

Rhubarb, Bourbon and Brown Butter Filling:

12 ounces rhubarb, trimmed, sliced on the diagonal 1/2″ thick (3 cups)

2 tablespoons organic cane sugar, plus 1/2 cup for the custard

8 tablespoons unsalted butter

1 vanilla bean, split lengthwise and scraped

2 eggs

1/4 cup all-purpose flour

1/4 teaspoon fine sea salt

2 tablespoons bourbon whiskey

Make the crust:

Position a rack in the lower third of the oven and preheat to 350º.

In the bowl of a food processor, process the almonds, powdered sugar, salt and flour until the almonds are finely ground. Add the butter, and pulse until the mixture just begins to clump together. Dump the crumbs into an 8 or 9-inch tart pan with a removable bottom. Don’t bother washing the food processor bowl. Press the dough into the sides of the pan first, then the bottom, taking time to make square corners, a neat top, and an even thickness. (If the dough becomes soft or sticky, put the whole pan in the refrigerator for 5-10 minutes to firm it up again.) Prick the bottom of the crust all over with a fork. Freeze the crust until firm, 15 minutes, or wrap for longer storage. 

Place the tart pan on a rimmed baking sheet for easy maneuvering, and bake the unlined crust until it is pale golden, 15-20 minutes, rotating after 10 minutes for even browning.

Meanwhile, make the filling:

Toss the sliced rhubarb with 2 tablespoons of the sugar in a medium bowl and set aside to macerate while you finish baking the crust and making the custard.

Place the butter and vanilla pod and scrapings in a medium, heavy-bottomed saucepan and cook over medium heat, swirling occasionally. After about 5-10 minutes, the butter will foam up, turn golden and smell nutty, with brown flecks mingling with black vanilla bean seeds. At this point, remove the pan from the heat. Remove the vanilla bean (you can rinse and dry it and stick it in a jar of sugar, or use it to make vanilla extract). Pour the butter into a heatproof measuring cup to stop the cooking, and let cool 5 minutes.

In the bowl of the food processor, pulse together the remaining 1/2 cup of sugar, the flour and salt to combine. Add the eggs, and process until combined. With the motor running, pour in the brown butter, including the brown flecks and vanilla seeds, then the bourbon. 

Assemble, bake, and eat the tart:

Scrape the rhubarb and any juices into the hot, par-baked tart shell in an even layer. Carefully pour the custard over the rhubarb, filling the shell to the brim.

Bake the tart until the filling is puffed and browned, 30-45 minutes, rotating the tart halfway through for even baking. Remove the pan from the oven and let the tart cool until warm. Set the tart on an inverted bowl or ramekin, and ease off the ring. Sprinkle the tart with powdered sugar, cut it into wedges, and serve warm or at room temperature.

The tart keeps well in the refrigerator for several days; re-warm slices in an oven or toaster oven for best results.