In the microwave, heat butter in a large microwave-safe bowl until very soft and partly melted.
Whisk in granulated and brown sugars. Let cool for a minute or two if your bowl is hot.
Whisk in egg, lemon juice, and vanilla.
In a separate bowl, whisk together flour, cornmeal, baking soda, lemon zest, and salt.
Stir dry ingredients into the wet ingredients with a sturdy wooden spoon.
Gently stir in blueberries.
Put bowl in the refrigerator and chill dough for 30 minutes.
Preheat oven to 350 degrees.
Line a baking sheet with parchment paper.
Scoop out cookie dough, then roll into balls with your hands.
Place 2 inches apart on the baking sheet.
Bake for 12-14 minutes, until just starting to brown around the bottom edges. Remove baking sheet from oven.
Let cookies sit for 2 minutes, then remove and let cool on a rack.
Notes
Storage Tips: Store cookies in an airtight container at room temperature. They will last for 3-4 days. You can also freeze these cookies. Fully cool after baking, then freeze in a ziptop freezer bag for up to 3 months. Defrost at room temperature before eating.Expert Tips: Using a cookie scoop makes scooping cookies so easy! We highly recommend this tool for all your cookie-baking needs. Watch how much time you let the cookie dough sit in the refrigerator before scooping. Cookies will get harder to scoop and roll the longer they chill. Try to be gentle when stirring in the blueberries. If you mash them as you are combining them, they will smear the dough purple.