Make the chocolate cake batter

• Whisk the chocolate cake mix, milk, melted butter, eggs and Greek yogurt until fully combined.
• Fold in the semi-sweet chocolate chips.

Prepare the Bundt pan

• Coat the inside of the Bundt pan with softened butter, spreading it evenly with a paper towel.
• Dust with cocoa powder, tossing it around until every surface is coated.

Bake the chocolate cake

• Pour the batter into the pan and tap it on the counter to release air bubbles and level it.
• Bake at 175 °C until a toothpick inserted in the center comes out clean.

Make the cookie dough

• Mix the melted butter with the white sugar and light brown sugar until combined.
• Beat in the egg and vanilla, then add the baking soda, baking powder and salt.
• Stir in the flour, then fold in the semi-sweet chocolate chips.

Bake the cookie cake

• Brush the cookie sheet with oil.
• Spread the dough evenly on the sheet with your hands.
• Bake at 175 °C until slightly golden brown but still soft in the middle.

Make the chocolate ganache

• Microwave the heavy cream with the semi-sweet chocolate chips in 30-second increments, stirring between each, until melted and smooth.
• Stir in a little extra heavy cream so the ganache flows down the sides.

Glaze the Bundt cake

• Pour the ganache over the cooled cake and let it drip down the sides.

Make the cookie cake icing

• Beat the room-temperature butter until creamy.
• Add the powdered sugar gradually and beat until smooth.
• Mix in the milk, vanilla and salt, adjusting with more milk or powdered sugar to the desired consistency.

Color and pipe the border

• Divide the icing into three bowls and tint each with a different food coloring.
• Spoon all three colors into a piping bag fitted with a star tip, without mixing them.
• Pipe a tri-color border around the edge of the cookie cake.