2½ cups (300 g) all purpose flour 

1 teaspoon cornstarch 

1 tsp baking powder 

¼ tsp baking soda 

½ tsp salt 

1½ cups (300 g) granulated sugar 

3 small or medium lemons, zested 

1 cup (226 g) unsalted butter, MUST BE ROOM TEMP

1 large egg (US), room temperature 

1 large egg yolk (US), room temperature 

1 tsp (5 ml) vanilla extract 

1 cup (105 g) fresh blueberries 

¼ cup (50 g) granulated sugar for rolling 

Preheat oven to 375 degrees. Mix Butter, eggs, vanilla, sugar and zest until smoooth. Add it dry ingredients until just combined. Fold in Blueberries. ~10 mins on preheated cookie sheet.