Preheat your oven to 350°F (175°C).
In a large bowl, cream together the softened butter and sugar until light and fluffy.
Add the egg, lemon juice, and lemon zest, mixing until well combined.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing just until incorporated.
Gently fold in the blueberries and white chocolate chips, if using.
Drop tablespoon-sized balls of dough onto a lined baking sheet.
Bake in the preheated oven for 12-15 minutes, or until the edges are lightly golden.
Allow the cookies to cool on the baking sheet for a few minutes before transferring to a wire rack.
Enjoy your delicious lemon blueberry cookies with a cup of tea or coffee!