Heat 1/4 cup heavy cream in a saucepan over medium heat until almost boiling. Remove from heat and stir in chopped chocolate until chocolate is melted and ganache is smooth. Refrigerate for 30 minutes.
Preheat oven to 350 degrees F (175 degrees C).
Combine remaining 1/4 cup cream, cubed panettone, eggs, milk, and sugar in a bowl and mix until well combined. Remove about 6 small tablespoons of panettone mixture and set aside.
Remove ganache from fridge and beat with an electric blender until creamy.
Grease a 6-cup muffin tin or line cups with paper liners. Spoon panettone mixture into the prepared muffin cups, filling each 3/4 full. Make an indention with your finger into each muffin and place 1 teaspoon of chocolate ganache inside. Cover with the 6 tablespoons panettone that were set aside.
Bake in the preheated oven until golden, 15 to 20 minutes.