Start by preheating your oven to 375°F (190°C). Line a large baking sheet with parchment paper. If needed, use two baking sheets to ensure enough space for the cookies. This prevents overcrowding and ensures even baking.

In a mixing bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, salt, and cornstarch. This mixture will provide the base for your cookie dough. Set this dry mixture aside for later.

Using an electric mixer, cream the softened butter with the light brown sugar and adjusted the amount of white sugar. Mix until the mixture becomes light and fluffy. This step helps to incorporate air into the dough, resulting in a soft and tender cookie texture.

Beat the large egg and vanilla extract into the butter-sugar mixture. Mix until the ingredients are just combined. Avoid overmixing at this stage.

Gradually add the prepared dry ingredient mixture to the wet mixture, using the electric mixer on low speed. Mix until the dough comes together. Be careful not to overmix, as this can lead to tough cookies.

Gently fold in the blueberries into the cookie dough. The vibrant blueberries will add bursts of flavor and color to your cookies.

Use a large cookie scoop to portion out the dough and place it onto the prepared baking sheet, leaving about 2 inches of space between each cookie. Place the baking sheet with the cookie dough in the refrigerator as you preheat the oven. Chilling the dough helps prevent excessive spreading during baking.

Once the oven is preheated, bake the cookies for 9-11 minutes (for smaller cookies) or 14-16 minutes (for larger cookies). The cookies should be golden brown around the edges while still looking slightly pale in the middle. Avoid overbaking to maintain a soft and chewy texture.

After baking, let the cookies cool on the baking sheet for 5-10 minutes. This allows them to set before transferring them to a wire rack to cool completely.

These Blueberry Cookies are best enjoyed while still warm, offering a delightful combination of flavors and textures. However, if you're saving them for later, store the cookies in an airtight container to maintain their moist and chewy quality. Though, with their irresistible taste, they're likely to disappear within the first day!