Heat the oil in a large saute pan over medium high heat.
Salt and pepper the pork cubes then add to the pan in a single layer. Let the meat brown on one side, then use tongs or chopsticks to flip them over and brown the other side. Transfer the pork to a bowl and turn the heat down to medium low.
Add the onions and cover with a lid for 10 minutes. Remove the lid and continue caramelizing the onions until they are dark brown and glossy (about 1 hour). Stir occasionally.
Add the browned pork, wine, water, carrots, potatoes, salt, tonkatsu sauce, tomato paste, applesauce, and black garlic oil then bring to a boil over high heat. Turn the heat down to medium low and simmer partially covered until the carrots are tender (about 45 minutes).
Meanwhile, make the roux by melting the butter over medium low heat. Add the flour, stirring while cooking until the mixtures turns a golden brown. Add the curry powder and black pepper and stir to incorporate (it will turn into a paste). Remove from the heat and set aside until the carrots are tender.
Make a batch of tonkatsu (breaded pork cutlets) or grill some vegetables to serve the curry sauce on.
Finish the curry by ladling some of the liquid the meat and veggies have been cooking in into the roux and whisk until there are no lumps. Pour this mixture back into the other pot and gently stir until the curry is thickened. Taste for salt and adjust as needed. When you’re happy with it, add the peas and chocolate and stir until the chocolate is melted and incorporated.
Slice the tonkatsu or portion the grilled vegetables and plate along with some cooked rice. Pour the sauce all over the plated food and serve.