Heat oven to 375°F and prepare two baking sheets (or cook in two batches) with parchment paper or a silicone baking mat.
Whisk together 1 1/2 cups powdered sugar, 1/3 cup cocoa powder, and 1/2 teaspoon kosher salt in a medium bowl until combined. In a small bowl, whisk together 1 large egg and 1 teaspoon vanilla extract until uniform.
Stir the egg mixture into the powdered sugar mixture. It will become a thick batter that resembles a thick chocolate frosting. Stir in the 1/2 cup semi-sweet chocolate chips and the 1/2 cup white or milk chocolate chips (or whatever chocolate you choose) until incorporated.
Using two spoons, scoop the batter into 1 Tablespoon balls onto the prepared baking sheet at least 2 inches apart. Bake for 8-10 minutes, until the tops appear glossy and cracked. Do not over bake.
Allow the cookies to cool on the baking sheet for at least 10 minutes before eating or storing. Store in an airtight container at room temperature for up to 3 days if needed.
Notes
You can use any combination of chocolate chips you want, using a total of 1 cup of chocolate chips. I like using half dark and half milk chocolate chips the best. You could even use Andes bits for a mint chocolate flavor, or Skor (or Heath) bits for a little toffee.Make sure to use dairy-free chocolate if you need these cookies to be dairy-free.