Rhubarb and Buttermilk Tart

Recently I saw a buttermilk pie being made on a television program and was reminded that buttermilk was often a base for a custard mixture. Buttermilk was on hand around a farm. Buttermilk is a by-product of making butter.  After the cream is churned and the butter is formed, the leftover liquid, the buttermilk, was left to ferment overnight and used for baking.

Today buttermilk is made by adding cultures to milk.

I thought that besides just a plain buttermilk pie or tart, why not put a layer of fruit under the custard as it bakes to complement the tangy quality of the buttermilk. And with rhubarb being the first “fruit” of the spring, I’ll begin with rhubarb. Rhubarb is not a fruit of course but a plant of which we use only the stem. Rhubarb is one of the first things to poke above the ground as the weather warms. Sour on its own, when sweetened just enough it becomes a flavorful give and take of sweet and tart.

You could use this idea as other fruit appears. For example, line the bottom of the tart with sliced ripe strawberries or blueberries.

For this year’s first tart, I have altered the basic pate sablee recipe to include brown sugar and some whole-wheat flour that adds a nice nuance of flavor to the completed tart.

Rhubarb Buttermilk Tart with Brown Sugar Sablee Crust

For one 10” tart

Pate sablee is close to cookie dough so it can be made the same way, either by hand or in a mixer. It doesn’t need to treated as carefully as standard pie crust. Any cracks can easily be patched.

Brown Sugar Sablee

¼ pound (1 stick) unsalted butter, at room temperature

½ cup dark brown sugar

1 egg

1 cup plain cake flour

1/3 cup whole wheat flour

¼ teaspoon salt

¼ teaspoon baking powder

1. Place the butter into a medium-sized bowl and beat until smooth. Add the sugar and blend until fluffy.  Mix in the egg, adding the flours, salt, and baking powder. Mix until all of the ingredients are combined. Remove dough from the bowl. Wrap in plastic wrap and refrigerate until needed.

2. When you are ready to use the dough, remove it from the refrigerator for 10 minutes to begin to soften. Working on a floured surface, cut the dough into pieces and knead together until the dough is smooth. Roll the dough out to 1/8^th” thickness; use extra flour to prevent the dough from sticking. Fit the dough into a tart pan with a removable bottom. Remove any excess dough by cutting it off of the edge of the pan. Using a fork, lightly prick the crust on the bottom and sides. Refrigerate before using.

3. To blind bake the tart shell: Heat oven to 350 degrees. Line the tart shell with a piece of aluminum foil. Fill the foil with rice, dried beans, or pie weights. Place the tart shell onto a baking tray and bake the tart shell for 15 minutes. Remove the pan from the oven. Carefully remove the foil with the rice/beans or pie weights. Return the empty tart shell to the oven and bake for 5 additional minutes. Remove and let cool. Any rice or dried beans used to line the foil can be saved and reused.

Rhubarb Filling

This can be made in advance and kept in a sealed container in the refrigerator until needed.

3 cups sliced rhubarb            

¼ cup sugar

2 Tablespoons water.

1. Place the rhubarb, sugar, and water into a medium-sized saucepan. Place the pan over low heat and stir. As the rhubarb begins to cook you can increase the heat beneath the pan. Cook the rhubarb until it has broken down and is the consistency of applesauce. Remove from heat and let cool. Taste and adjust the sweetness to your liking, but it’s best if it’s sweet and tart.

Buttermilk Custard

3 eggs

2 Tablespoons sugar

½ teaspoon vanilla

1 ½ cups buttermilk

1. Heat oven to 350 degrees. Place the eggs into a bowl and whisk until smooth. Add the sugar and vanilla and buttermilk and whisk until combined and smooth. When the oven is hot, place the partially baked tart shell onto a baking tray. Spread the rhubarb filling onto the shell. Pour the buttermilk custard to cover the rhubarb; you may have 2 to 3 tablespoons of leftover custard. Carefully place the tray with the tart into the oven bake for 30 to 35 minutes, until the custard is set; it may wiggle slightly, but that’s fine. Remove from oven, let cool, and serve.