Prepare your oven and equipment. Preheat your oven to 350°F (175°C). Line two cookie sheets with parchment paper to prevent sticking and ensure easy cleanup.
Mix the dry ingredients. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well combined. This ensures even distribution of leavening agents throughout your cookies.
Cream the butter and sugars. In a large bowl, beat the softened butter with both sugars using an electric mixer on medium speed for about 2-3 minutes until light and fluffy. This incorporates air into the batter for a better texture.
Add the wet ingredients. Beat in the eggs one at a time, then add the lemon juice, lemon zest, and vanilla extract. Mix until just combined – the mixture might look slightly curdled due to the lemon juice, but don’t worry!
Combine wet and dry mixtures. Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Over-mixing will develop too much gluten and make your cookies tough.
Fold in the blueberries. Gently fold in the blueberries (and white chocolate chips if using) with a rubber spatula. Be careful not to crush the berries, especially if using fresh ones, to avoid purple streaking throughout the dough.
Scoop the dough. Using a cookie scoop or tablespoon, drop rounded portions of dough onto the prepared cookie sheets, spacing them about 2 inches apart. These cookies will spread moderately during baking.
Bake to perfection. Bake in the preheated oven for 12-15 minutes, or until the edges are just turning golden but the centers still look slightly underdone. They’ll continue cooking slightly after removal.
Cool properly. Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. This allows them to set up without breaking.