• Line two baking sheets with parchment paper.
• In the bowl of a stand mixer (or using a hand mixer), cream the room-temperature butter, sugar, and optional citrus zest if using, together on medium-high speed for 2–3 minutes, until light and starting to get fluffy - don't overwhip or they will be too cakey.
• Add the egg, vanilla extract, and lemon extract, and mix until fully incorporated.
• In a separate bowl, whisk together the gluten-free flour, cornstarch, baking powder, baking soda, and salt. Add the dry ingredients to the wet ingredients and mix until a soft dough forms.
• Gently fold in the fresh blueberries by hand, trying not to break them. I prefer using smaller blueberries here so the cookies hold their shape and don’t get too wet.
• Using a large cookie scoop or your hands, portion the dough into 8 large bakery-style cookies (about 100g each) or 16 regular-size cookies (about 50g each). Roll each dough ball gently to smooth the surface.

Optional: Citrus Sugar Coating

• If you’re rolling the cookies in citrus sugar, combine 100 g granulated sugar with 1 teaspoon of finely grated lemon or lime zest in a small bowl. Rub the zest into the sugar with your fingers to release the oils. Roll each dough ball lightly in the citrus sugar before placing on the baking sheet.
• Space the dough balls about three inches apart on the prepared baking sheets and rest at room temperature for 30 minutes while your oven preheats. *see note
• Preheat your oven to 350°F (175°C).
• Slightly press down on the dough balls before putting in the oven. Bake for 11–13 minutes for regular-size cookies or 12–15 minutes for larger cookies, until the edges are just set and lightly golden. The centers will still look soft.

Important:

• While the cookies are still warm and puffy, use a round cutter, jar ring, or an upside down bowl, to scoot them into a perfect circle. This gives them that signature bakery look. Let them cool completely on the baking sheet so the centers finish setting and stay soft.

Optional Glaze:

• In a small bowl, whisk together 100–120g powdered sugar, 1 tablespoon blueberry juice or purée, and 1 tablespoon lime or lemon juice. Adjust the thickness by adding more sugar for a thicker glaze or a few drops of juice to thin it out. Add zest for extra citrus punch, if desired.
• Drizzle the glaze over the cooled cookies using a spoon or piping bag. Let set before stacking or storing.