Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, combine the cream cheese, butter, egg, lemon zest, 1 tablespoon (15 ml) lemon juice, baking powder, and vanilla extract. Use a hand mixer on medium speed to beat until smooth and fully combined.
6 oz (170 g) full-fat cream cheese, ½ cup (113 g) European-style butter, 1 large egg, zest from 1 lemon, 5 tbsps (75 ml) fresh lemon juice, 1 tsp (4 g) baking powder, ½ tsp (2.5 ml) vanilla extract
Add the lemon cake mix to the bowl. Mix on low speed just until the batter comes together.
1 box lemon cake mix
Stir in the white chocolate chips with a spoon or spatula until evenly distributed.
½ cup (85 g) white chocolate chips
Gently fold in the blueberries, being careful not to crush them.
1 cup (150 g) fresh blueberries
Using a medium cookie scoop (filled about 75% full, or approximately 2 tablespoons / 30 ml), place dough onto the prepared baking sheets, spacing them 2 inches (5 cm) apart.
Bake for 10 to 13 minutes, or until the cookies are set but not browned. The centers may still look slightly soft.
Let the cookies cool on the baking sheet for at least 10 minutes.
In a small bowl, whisk together the confectioners’ sugar and 2 to 4 tablespoons (45 to 60 ml) of lemon juice, adding the juice gradually until the glaze reaches your desired consistency.
1 cup (120 g) confectioners' sugar
Drizzle the glaze over the cooled cookies with a spoon. Let them sit until the glaze is set.