Start by browning the butter. This step can be done ahead of time, too. Cube the butter into small cubes and place it into a small saucepan.
Melt the butter over medium heat. Once the butter has melted and begins to simmer, reduce the heat to a medium-low. The butter will become foamy at first – this is the milk solids separating from the butter.
As you continue to cook the butter, the foam will settle, and the milk solids will sink to the bottom of the pot. As the butter cooks further, it will begin to foam for a second time, and you’ll begin to see small brown flecks.
Cook until the butter turns a golden-brown color, then remove it from the heat. Strain the butter through a fine-mesh strainer into a large measuring cup.
Chill the browned butter in the refrigerator for about 1 to 1 ½ hours, until it’s cooled down to room temperature. The butter should still be liquid.
Making the Cookie Dough:
Preheat the oven to 375F°. The oven needs to be preheated for at least 20 minutes before baking cookies. Line a large baking sheet with parchment paper or a silicone mat.
Pour the cooled, browned butter into a large mixing bowl. Add the white and brown sugars, then use a mixer to cream the butter and sugar together for about 4 minutes, until smooth and creamy.
Next, add in the eggs and vanilla and beat again for a few minutes.
In a separate bowl, combine the flour, baking soda, sea salt, and dried milk powder. Add the dry ingredients to the creamed butter and mix just until well combined and no dry flour remains.
Add the white chocolate chips and chopped pistachios last and fold them into the cookie dough with a spatula.
Once you have the cookie dough ready, you can bake the cookies right away. Use a large measuring scoop (1 ½ tablespoons) to measure out the dough for each cookie.
Drop the cookie dough onto the prepared baking sheet, spacing the cookies a few inches apart. I usually fit 9 cookies onto a half-sheet pan.
Baking Instructions:
Bake the cookies at 375F° for exactly 10 minutes. If your oven runs hot, reduce by 30 seconds to a minute. The cookies should be just golden brown around the edges and slightly soft and underdone on the top.
Remove the cookies from the oven and immediately sprinkle with sea salt flakes. Use the bottom of a large measuring cup or glass and gently press and flatten each cookie.
Use a large, round cookie cutter or glass to shape and twirl each cookie into a nice, round shape. This also helps thicken the edges of the cookies.
Transfer the cookies onto a wire rack to cool completely.
Serving & Storing:
Allow the cookies to cool down a bit before enjoying as the chocolate will get very hot during baking. Enjoy these cookies with coffee, tea, or a glass of milk.
Store any leftover cookies in an airtight container at room temperature. For freezing the cookies, wrap them in plastic first before placing into an airtight freezer container.