Whisk together flour, baking soda, and salt in a medium bowl. Set aside.
Cream together butter, white sugar, and brown sugar in a large bowl with an electric mixer on medium speed until light and fluffy (about 3 minutes). Add egg and vanilla; beat well. Gradually add the flour mixture just until combined, being careful not to overmix. Stir in the white chocolate chips and the dried cranberries.
Drop batter by heaping tablespoons onto ungreased or parchment lined baking sheets.
Bake for 8-10 minutes, or just until lightly browned on the edges but still soft in the centers.
Allow the cookies to cool on the cookie sheets for at least 1-2 minutes, and then transfer them to wire racks to cool completely.
Make sure that the butter and egg are at room temperature so that they mix together smoothly.
The key to maintaining those decadent, soft, centers in your double chocolate chip cookies is not overbaking. Remove the cookies from the oven just as the edges are starting to brown. Thecenters will still look soft and under-baked, but the cookies will continue to firm up as they cool.
You don't need to chill the dough before baking (unless your house is really hot and humid). However, if you prefer a thicker cookie that spreads less in the oven, chill the dough for at least 2 hours (or up to overnight).
Some folks prefer fewer chunky add-ins, so feel free to reduce the amount of white chocolate chips that you mix into the dough.
For an ultra-chewy texture, add an extra egg yolk to the dough. You can also swap out half of the all-purpose flour for bread flour, which has a higher protein content and therefore creates a chewier bite.
If you prefer a crispy cookie, use more granulated sugar than brown sugar and bake the cookies for a few extra minutes.