Preheat oven to 350°F and line a cupcake tin with paper liners.
In a large bowl, whisk together 1⅓ cups flour, 2 cups sugar, 1 cup cocoa, 1½ teaspoons baking soda, 1½ teaspoons baking powder, and 1 teaspoon salt.
In a separate bowl, whisk together 2 eggs, 1 cup whole milk, ½ cup oil, and 2 teaspoons vanilla.
Pour the wet ingredients into the dry ingredients and mix until combined. Beat the batter on medium speed for 3 minutes.
Reduce mixer speed to low and slowly add 1 cup boiling water, starting with a small amount and then pouring the remaining water while mixing. The batter will be thin.
Fill each paper-lined cup about ¾ full with batter. Bake 20 to 25 minutes, or until a toothpick inserted in the center comes out clean.
Remove cupcakes from the oven and let them cool in the pan for 10 minutes. Transfer cupcakes to a wire rack and let them cool completely.
For the frosting: beat 1 cup unsalted butter until smooth. Gradually add 4 cups powdered sugar and beat until the mixture is light and creamy.
If the frosting is too stiff, add up to 4 tablespoons heavy whipping cream a few drops at a time until it reaches a spreadable consistency. If needed during mixing, add the powdered sugar gradually from the measured 4 cups to reach the desired thickness.
Test the frosting by placing a spoonful on a spoon and turning it upside down; the frosting should stay on the spoon. Adjust only with the measured powdered sugar or the measured heavy cream as described above.
Add blue gel coloring a small amount at a time and mix until you reach the desired shade of blue.
Spoon the frosting into a pastry bag fitted with a large star tip, twist the open end to push the frosting toward the tip, and hold the bag straight up and down when piping.
Pipe the frosting straight up and down onto each cooled cupcake.
Place the 2 large candy eyes on top of a frosted cupcake.
Cut the 1 chocolate chip cookie in half and stick one cookie half into the middle of the frosted cupcake so it looks like it is sticking out of the mouth.