Line 2 large baking sheets with parchment paper or silicone baking mats. Preheat the oven to 350°F (175°C).

In a medium bowl, whisk together the flour, baking soda, baking powder, and salt until well combined. Set aside.

In a large mixing bowl, beat the softened unsalted butter, salted butter, brown sugar, and granulated sugar with a hand mixer or stand mixer on medium speed for 2–3 minutes, until light and fluffy. Scrape down the sides of the bowl as needed.

Beat in the eggs one at a time, mixing well after each addition. Add the vanilla extract and mix again until the mixture looks creamy and well blended.

Add the dry ingredients to the wet ingredients in two additions, mixing on low speed just until the flour is incorporated. If the dough looks crumbly or too stiff, add 1–2 tablespoons of milk or cream and mix briefly until it comes together; do not overmix.

Using a spatula, fold in the white chocolate chips and dried cranberries until evenly distributed. If using, gently fold in nuts or spices as well.

Cover the bowl and chill the dough in the refrigerator for at least 30–60 minutes, or up to 48 hours. If chilling longer than 2 hours, let the dough sit at room temperature for 10–15 minutes before scooping so it’s easier to handle.

Use a 1 1/2 to 2 tablespoon cookie scoop (about a heaping tablespoon) to portion the dough onto the prepared baking sheets, spacing the scoops about 2 inches apart. For a bakery-style look, roll each scoop into a ball and gently press a few extra white chocolate chips and cranberries on top, if desired.

Bake in the preheated oven for 9–12 minutes, or until the edges are set and lightly golden while the centers still look soft and slightly underbaked. Rotate the pans halfway through baking if your oven has hot spots.

Remove the baking sheets from the oven and let the cookies cool on the pans for 5–10 minutes. If desired, sprinkle a tiny pinch of flaky sea salt on top while the cookies are still warm. Transfer to a wire rack to cool completely.