Rhubarb Thumbprint Cookies

Thick chewy sugar cookies baked with a center of homemade vanilla rhubarb jam in the center.

Prep Time 30

Cook Time 12

Chill Time 4

Servings cookies

400g g rhubarb chopped (about 3 large stalks), weighed after stems and leaves removed
120g fine granulated sugar about ½ cup plus 2 tablespoons
1 ½ tablespoons tapioca starch or cornstarch
Pinch fine sea salt
1 vanilla bean split (optional)

200 or 1 cup cup granulated sugar
zest of 2 lemons
226g or 1 cup butter unsalted
2 teaspoons pure vanilla extract
1 teaspoon fine sea salt
65 or ½ cup powdered sugar
1 large egg
½ teaspoon baking soda
390g or 3 cups all purpose flour if using cup measurements, shake the flour over the measuring cup and level it - never pack it in
Powdered sugar for sprinkling on top if desired

Remove the leaves (any green part) from the rhubarb and chop into 1 inch pieces. Set a pot over medium low heat and to it add the rhubarb, sugar, starch, salt and vanilla bean, if using (for the vanilla bean: slice the bean down the middle and pry the sides open like a book, scrape down to gather the caviar and add the bean and it’s scrapings to the pot).
Cook slowly, stirring occasionally to ensure the rhubarb doesn't burn at the bottom of the pan. As it cooks the rhubarb will break down, once it’s very soft remove the vanilla bean pod and puree the mix (you can do this with an immersion blender right in the pot or transfer to a food processor or blender). Press the puree through a fine mesh sieve, take your time doing this and squeezing out all the fruit while leaving the stringy bits behind.
Transfer to an airtight container and store in the fridge for at least a few hours before using but up to a week.

Set the granulated sugar in a heatproof bowl and zest the lemons over it. Rub the lemon zest into the sugar with your fingers. Set the butter in the bowl and place it in the microwave for 60 seconds (use a microwave plate to cover the butter so it doesn’t sputter out) until melted.
Whisk the butter and sugar together vigorously. Add the salt and vanilla and whisk well. Sift in the powdered sugar then whisk until the mix is thick and cohesive.
Add the egg and whisk well then stir in the flour and baking soda until the flour is all incorporated. Cover with plastic wrap (or transfer to an airtight container) and chill in the fridge for 3-4 hours or overnight.

Preheat the oven to 350 F and line two greased cookie sheets with parchment paper.
Use a disher to scoop the cookies into about 2 tablespoons per cookie (you can make them smaller or bigger but they need to hold enough jam), ensuring you have a rounded ball and leaving enough space for them to spread. Press the cookie dough in the middle with a rounded tablespoon or your thumbs until you have a tiny bowl shaped indentation (careful not to go too deep that you have a too thin layer on the bottom of the cookie). Pour in about a half tablespoon of jam (or however much works for your chosen size of cookie). Round the cookies with your hands and add a bit of dough to anywhere a crack might appear; this way none of the filling seeps out in the oven.
Bake for about 12 minutes, until the cookies are just turning golden on the edges. Let cool on a pan then transfer to a plate to serve. Before serving, sprinkle the cookies with powdered sugar, if desired.