In a large bowl using a handheld mixer or stand mixer with paddle attachment, beat the butter, brown sugar, and granulated sugar together on medium speed until combined and creamy, about 3 minutes. Beat in the egg and vanilla. Scrape down the sides and bottom of the bowl and beat again as needed to combine.

In a separate bowl, whisk the flour, cornstarch, baking soda and salt together. On low speed, slowly mix into the wet ingredients until combined. The cookie dough will be soft and thick. Add the white chocolate chips and dried cranberries and beat on low speed until combined. Cover dough tightly and chill in the refrigerator for at least 1 hour and up to 3-4 days.

Remove cookie dough from the refrigerator. If the cookie dough chilled longer than 3-4 hours, let it sit at room temperature for about 30 minutes.

Preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats.

Scoop and roll dough, about 1.5 Tablespoons (35g) of dough each, into balls. Arrange dough balls 3 inches apart on the prepared baking sheets.

Bake for 11-12 minutes or until lightly browned around the edges. The centers will still look soft.

Allow cookies to cool on the baking sheet for 5 minutes. During this time, press extra white chocolate chips and dried cranberries into the warm tops.

Transfer to a wire rack to cool completely.

Cookies stay fresh covered at room temperature for up to 1 week.