Rhubarb Cookies with Vanilla Rhubarb Jam Thumbprints

Add rhubarb and sugar to the bottom of a saucepan. Cook, stirring over medium heat, until the sugar is dissolved and the rhubarb starts to release its juices.
Bring the mixture to a boil. Continue to cook over medium heat, maintaining a boil, for 7 minutes. Stir occasionally to prevent the jam form boiling over.
Once the jam is thick and glossy and the rhubarb has broken down into soft threads remove the jam from the heat and allow it to cool. Stir in the vanilla extract.

Preheat the oven to 375°F and line cookie sheets with parchment paper.
Cream the butter until it is light in color and fluffy in texture, about 3 minutes at full speed with an electric mixer.
Add the flour and powdered sugar and mix on low speed until well incorporated and crumbly.
Add in the eggs and vanilla and mix on medium speed until the dough comes together. If necessary, use your hands or a wooden spoon to bring the mixture completely together into a ball.
Roll out tablespoonfuls and coat them with granulated sugar. Place them on the prepared sheet about 2 inches apart.
Using a small ½-teaspoon measuring spoon, melon baller, or your thumb, make a well in each cookie. Coat the spoon in sugar to prevent sticking.
Fill a piping bag or zip bag with the jam and pipe the jam into the well, being careful not to overfill.
Bake for 12-14 minutes, until the edges are golden. Transfer the cookies to a cooling rack to cool completely. Store completely cooled cookies in an airtight container.