1 1/2 Tbsp lemon zest (from about 3 medium lemons)
1 large egg
1 tsp lemon extract
1/2 tsp vanilla extract
1 1/3 cups white chocolate chips
Preheat oven to 350 degrees. In a mixing bowl, whisk together flour, baking soda, salt and cornstarch for 20 seconds, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment, cream together butter, granulated sugar, brown sugar and lemon zest (not until pale and fluffy, just creamy). Mix in egg, then mix in lemon extract and vanilla extract (if you want the cookies a little more yellow, you can add a few drops of yellow food coloring when adding the extracts). With mixer set on low speed slowly add in dry ingredients and mix until combined, then mix in white chocolate chips.
Scoop dough out 2 1/2 Tbsp at a time and shape into balls (I used a 1 1/2-inch cookie scoop and filled heaping). Place on Silpat or parchment paper lined baking sheets, spacing cookies 2-inches apart. Bake in preheated oven 10 - 12 minutes (cookies should look slightly under-baked, they will continue to cook slightly once removed from oven). Cool on baking sheet 2 minutes (if desired, you can lightly press more white chocolate chips into tops immediately after removing from oven) then transfer to a wire rack to cool. Store in an airtight container.