Preheat oven to 350 degrees F (175 degrees C). Line a 9x13-inch baking pan with aluminum foil; spray with cooking spray.
Stir sugar, flour, cocoa powder, baking powder, baking soda, and salt together in a large bowl. Add 1 cup milk, oil, eggs, and vanilla extract; mix until batter is smooth. Stir in boiling water. Pour batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Cool until easily handled, at least 30 minutes.
Crumble cake into a bowl; mix in crushed cookies. Add milk, 1 tablespoon at a time, until cake mixture sticks together. Shape into balls. Line a baking sheet with plastic wrap; arrange cake balls on the sheet and freeze until firm, about 15 minutes.
Melt 1/2 cup chocolate coating in a microwave-safe bowl in 15-second intervals, stirring after each melting, 1 to 3 minutes. Dip the tip of each cake pop stick into the melted chocolate and insert halfway into a cake ball. Arrange cake pops upside-down on the baking sheet; freeze until chocolate hardens, about 15 minutes.
Melt the remaining chocolate coating in a deep microwave-safe bowl in 15-second intervals, stirring after each melting, 1 to 3 minutes. Dip each cake pop entirely into the melted chocolate; tap lightly on the side of the bowl to shake off excess chocolate. Repeat with the remaining cake pops. Stick upright into a foam board until set, at least 20 minutes.