Sift together the flour, cocoa powder, espresso powder, baking soda, baking powder, and salt in a medium bowl. Sifting removes lumps and aerates the dry ingredients, which helps create a lighter texture in the final cookies. Set this mixture aside—you'll add it to the wet ingredients later.

While you're getting organized, melt the 1.33 cups of semi-sweet chocolate chips in a microwave-safe bowl in 30-second intervals, stirring between each interval until completely smooth. In a large mixing bowl, beat the room-temperature butter with the granulated sugar and brown sugar for 2-3 minutes until light and fluffy—this aerates the mixture and creates a better cookie texture. I like to use room-temperature butter because it creams more easily and incorporates air better than cold butter, giving you fluffier cookies.

Pour the melted chocolate from Step 2 into the creamed butter and sugar mixture, beating until fully incorporated. Add the room-temperature eggs one at a time, beating well after each addition, then mix in the vanilla extract. The eggs emulsify the dough and add structure, while the chocolate creates the rich flavor base for your cookies.

Gradually add the dry ingredient mixture from Step 1 to the wet mixture from Step 3, stirring on low speed until just combined—don't overmix, as this can make cookies tough. Fold in the milk chocolate chips, the remaining semi-sweet chocolate chips, and the chopped toasted walnuts by hand using a spatula or wooden spoon. I find that folding in the mix-ins by hand gives me better control and prevents overdeveloping the gluten.

Using a cookie scoop or spoon, form dough into 1.5-inch balls and place them on a parchment-lined baking sheet. Cover the sheet with plastic wrap and refrigerate for at least 2-3 hours—this resting period allows the flavors to develop and prevents the cookies from spreading too much during baking. Chilling dough is key to getting that signature crinkled texture.

Preheat your oven to 350°F. Sift the powdered sugar into a shallow bowl. Working with one chilled dough ball at a time, roll it in the powdered sugar until evenly coated, then place it on a parchment-lined baking sheet about 2 inches apart from other cookies. Bake for 18-20 minutes—the edges will be set but the centers should still look slightly underbaked and fudgy. The powdered sugar coating creates that distinctive crinkled appearance as the dough rises and cracks in the oven.

Let the cookies cool on the baking sheet for 5 minutes to set slightly, then transfer them to a wire cooling rack to cool completely. This brief rest on the sheet prevents them from breaking, while moving them to the rack allows air circulation for even cooling.