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 and drained rice cakes, 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 some chopped green onion over the top. Ladle some of the tteokbokki, egg, and sauce into two bowls. Serve immediately.