1.In a large bowl, soak rice cakes in cold water for 1 hour. Meanwhile, combine gochujang, gochugaru, soy sauce, sugar, milk, heavy cream, and 1/2 cup water in a medium bowl. Whisk well until it has no lumps, set aside. Drain the rice cakes.
2.Heat up a large skillet over medium heat. Add bacon and stir for about 5 minutes until crispy and golden brown. Turn the pan off and discard the excess fat from the bacon.
3.Turn the heat to medium-high on the same skillet. Add the garlic and onion to the bacon and stir for 1 minute. Add the sausage stirring for a minute until the sausage splits a little along the slits.
4.Add the rice cakes and 1 cup water to the skillet and stir. Cover and cook for 5 minutes until the rice cake are tender. Open the lid and add the sauce, mixing well. Cook another 5 minutes, stirring occasionally.
5.Add mozzarella and stir until the cheese is melted. Sprinkle the green onion over the top. Ladle some of the tteokbokki, egg, and sauce into bowls. Serve immediately.