Cut the quinces in quarters, clean and cut each piece in 3 smaller pieces. Put them in a non-stick pan and sauté them lightly with butter. Pour in the orange juice and add 200 ml of warm water, cover the pan with a lid and simmer the quinces for about 30 minutes, until they are tender. Sprinkle with sugar, and leave them for 10 minutes to caramelize over the heat. Leave them aside until the pork is ready.
Cut the pork into large cubes, season them and dust them with flour. Skip the excess of flour. In a large saucepan, heat up the olive oil and sauté the meat well from all sides until it is well browned. Add the chopped onion, continue sauteing until it is glistening and slightly softened. Add the tomato paste and the coriander, sauté lightly and pour in the wine. Pour 200 ml of warm water and let the meat boil for about 1½ hours. If the liquids have been saved in between and the meat has not been done yet, add some warm water. Then put the quinces over the meat with the juice and simmer at low temperature for about 10 minutes to mix their flavors. Rotate the pot, but do not stir the food, because the quinces will melt. Add the carob syrup the last 5 minutes. Remove the food from heat, let it sit for 5 minutes and serve.