Zest and juice the lemon. In a small bowl, weigh or measure the sugar and set it aside. In a medium bowl, weigh or measure the flour, baking powder, and kosher salt, then whisk until well combined.
In a stand or handheld mixer, beat the cream cheese and butter on medium speed for 1 minute until smooth.
Add the sugar and continue mixing on medium speed for 3 minutes until light and creamy. Scrape down the sides and bottom of the bowl to ensure everything is evenly combined.
Add the egg and mix until fully incorporated. Add the lemon zest and juice and mix until combined.
Turn the mixer to low speed and add the flour mixture about one-third at a time, mixing just until incorporated after each addition. Scrape down the sides and bottom of the bowl to make sure everything is evenly mixed.
Add the dried blueberries and mix for about 5 seconds. I take a spatula and make sure the blueberries are evenly distributed into the cookie dough.
Cover the bowl and refrigerate the dough for 1 hour. Remove the dough from the refrigerator about 10 minutes before scooping the cookies.
Preheat the oven to 350°F (175°C or 180°C) and line two cookie sheet pans with parchment paper.
Using a medium cookie scoop, portion the dough and roll each scoop into a smooth ball. Place 12 cookie dough balls on a prepared cookie sheet, spacing them evenly apart.
Press your thumb straight down into the center of each cookie dough ball to make a well for the blueberry preserves. Be careful not to press all the way through the bottom of the cookie. If the dough starts sticking to your thumb, wipe it with a damp paper towel between cookies. After making the thumbprint, I gently go around the edge with my finger to widen the well just enough to hold a little more blueberry preserves.
Fill each thumbprint with blueberry preserves or jam, being careful not to overfill. Bake for 11 to 13 minutes, checking the cookies at 11 minutes. The cookies are done when they are just firm to the touch. Transfer them to a cooling rack immediately. Once cooled, dust with powdered sugar, if desired.