1. Sauté the ground Hanwoo beef and bacon slices in a pan, then deglaze with red wine.
2. In another pan, heat olive oil and sauté minced garlic, diced onion, carrot, celery, and tomato paste until the acidity is cooked off.
3. Add Step 1 and Step 2 together in a pot. Then, add Reggiano rind, whole tomatoes, bay leaf, thyme, salt, and sugar, and simmer until the sauce reaches a thick consistency. Stir in grated Grana Padano
4. Slice the croissants in half and top with mozzarella cheese. Toast in an oven until the cheese slightly melts.
5. Fill the croissants with the Bolognese sauce, sprinkle with Grana Padano cheese, and toast again until golden brown.