Preheat oven to 375 degrees. Line baking sheets with parchment paper.

With an electric mixer, beat the butter, granulated sugar, and brown sugar at medium speed until fluffy, 3-4 minutes. Beat in egg, lemon zest and vanilla.

In a medium bowl, whisk together flour, baking powder, and salt. With mixer on low speed, add flour mixture to butter mixture in two additions, alternating with all of sour cream, and beginning and ending with the flour mixture.

Gently fold in blueberries. Scoop or spoon 1/4 of batter onto prepared pans, about 3 inches apart. Sprinkle with sparkling sugar if using.

Bake until a wooden pick inserted in center comes out clean, about 15 minutes. Let cool on pans for 5 minutes before removing to wire racks to cool completely.

Meanwhile, whisk together the confectioners sugar and lemon zest in a medium bowl. Gradually whisk in lemon juice until glaze reaches desired consistency. Drizzle over cooled cookies.