Preheat oven to 350°F. Butter an 8x8-inch baking pan and set aside.
In a medium mixing bowl, whisk together the flour, ⅔ cup sugar, ¼ cup cocoa powder, baking powder, and salt until combined.
1 cup all-purpose flour, 1⅔ cups granulated sugar, 6 tablespoons unsweetened cocoa powder, 2 teaspoons baking powder, ½ teaspoon kosher salt
In a separate bowl, whisk together milk, butter, and vanilla until smooth.
½ cup milk, 6 tablespoons unsalted butter, 1 teaspoon pure vanilla extract
Add the wet mixture to the dry mixture and stir to combine into a thick batter.
Pour the batter into the prepared baking dish.
In a small bowl, stir together the remaining sugar and cocoa powder.
Sprinkle the sugar mixture evenly over the batter.
Sprinkle on the chocolate chips.
¾ cup chocolate chips
Slowly pour the boiling water over the top of the mixture without stirring.
1½ cups boiling water
Bake for 30-40 minutes, until the center is just set. Serve slightly warm with ice cream and nuts, if desired.
vanilla ice cream