01 -
Add blueberries, sugar, lemon juice, vanilla, and cornstarch to a medium saucepan. Cook over medium-low heat for 30-40 minutes until the mixture thickens to 1/2 cup (120 ml). Smush some blueberries with the back of a wooden spoon around 15 minutes into cooking. Remove from heat and cool completely.
02 -
Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper and set aside.
03 -
In a large bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
04 -
In a large mixing bowl, cream together softened butter and granulated sugar with an electric mixer on high speed until fluffy, about 2 minutes.
05 -
Mix in the egg and vanilla on medium speed until the mixture is pale and fluffy, about 1-2 minutes.
06 -
Gradually add the dry flour mixture to the wet mixture. Mix on low speed until just combined, scraping down the sides of the bowl as necessary.
07 -
Gently fold the cooled blueberry jam into the dough using a rubber spatula.
08 -
Scoop the dough into balls using a 2-tablespoon cookie scoop. Place them on prepared baking sheets.
09 -
Optionally sprinkle cookies with additional granulated sugar. Bake in batches of 6 cookies at a time for 10-13 minutes. Let the cookies cool on the baking sheet for 5 minutes, then transfer to a cooling rack.