185 g all purpose flour*
1 tbsp corn starch
½ tsp baking powder
¼ tsp baking soda
¼ tsp salt
115 g unsalted butter, softened slightly but still cool
130 g granulated sugar
2 tbsp finely grated lemon zest (1 large lemon's worth)
1 tsp pure vanilla extract
1 large egg + 1 large egg yolk
1½ tbsp freshly squeezed lemon juice
80 g white chocolate chips or chunks
Combine flour, cornstarch, baking powder, baking soda, and salt.
Beat butter, sugar, and lemon zest until creamy and combined, about 1 minute. Add vanilla, egg, egg yolk, and lemon juice, beating until combined and scraping the sides and bottom of the bowl as needed. The mixture might look a little curdled, that's ok. Add the flour mixture and beat until well combined. Stir in the white chocolate chips. Place the dough in the refrigerator for one hour.
Preheat oven to 180°C. Line two baking sheets with baking paper (this is important so that the cookies don't spread too much).
Scoop the chilled dough into 2-tablespoon balls. Place the dough balls a 6-7 cm apart on the baking sheets. For thicker cookies leave the dough balls mounded, for thinner cookies press down on each dough ball (jut a bit!) to encourage spreading. Bake for 11 minutes. The edges should just be beginning to set and the center should still look slightly underdone. If desired, place a few extra white chocolate pieces on top of each cookie (the heat from the cookie will make the chocolate melt and stick). Let cookies cool completely before removing from baking sheet - they will firm up as they cool.