Preheat the oven to 350°F (175°C). Line a large baking sheet with parchment paper.
In a stand mixer fitted with a paddle attachment or using an electric hand mixer, cream the room-temperature butter and light brown sugar for 2–3 minutes until soft and smooth. Scrape down the sides of the bowl as needed.
Add the milk and vanilla extract. Mix until incorporated.
Add the all-purpose flour, cornstarch, salt, and baking soda. Mix until just combined and a soft cookie dough forms. Avoid overmixing.
Add the white chocolate chips and dried cranberries. Mix until evenly distributed.
Divide the dough into 12 equal portions, approximately 50 g each, using a medium cookie scoop or about 3 tablespoons of dough per cookie.
Roll each portion gently between your hands to form a smooth dough ball.
Arrange the dough balls on the prepared baking sheet, leaving enough space between them for spreading.
Bake for approximately 10 minutes, or until the edges are lightly golden. The centers may still look slightly soft.
Allow the cookies to cool completely before serving. They will continue to set as they cool.
Store completely cooled cookies in an airtight container at room temperature for up to 4–5 days.