Preheat the oven to 400 F. Line two cookie sheets with parchment paper.
Pour the sugar into a large mixing bowl and zest the lemons over it. Rub the zest into the sugar with your fingers for a few minutes, to release the oils.
Add the butter, salt, baking soda, vanilla, and lemon extract and beat on medium speed with an electric mixer. Beat until airy and well creamed, for about 3-5 minutes.
Add the egg, and egg yolks and beat until creamy. Add the flour, starch and beat until half combined. Add the blueberries (in the video I tossed my blueberries in the starch but this isn't necessary) and white chocolate chips to the bowl. Switch to using a rubber spatula (or your hands) to gently mix the berries and chocolate in, careful not to burst any of the berries. Stop as soon as the dough is evenly mixed.
Use the spatula to spoon out a scoop of dough that’s around 100g (about a quarter of a cup) and place it on the prepared cookie sheet. You’ll have enough for 11 large cookies. Alternatively make even bigger cookies that are 150g each (these will need to bake longer). Leave enough space around the cookie balls for them to spread, at least an inch.
Bake the first batch of cookies on the lower rack of the oven, closer to the heat source, for 9-10 minutes (this will help the edges set quicker) then transfer to the middle rack for an additional 2-3 minutes, until golden and the cookies look dry in the middle (not doughy). Let them cool on the pan. Bake the second batch the same way.
Store cookies in an airtight container. They’re best within 24 hours of baking.