In a food processor or blender, combine the chopped onion, garlic, ginger, galangal, soaked red chilies, turmeric, and 1 tablespoon of vegetable oil. Blend until a smooth paste forms, scraping down the sides as necessary.

Heat the remaining 1 tablespoon of vegetable oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add the beef chunks in a single layer and sear until browned on all sides, about 5 to 7 minutes. Remove the beef and set it aside.

Reduce the heat to medium and pour the blended spice paste into the pot. Sauté the paste for 3 to 5 minutes, stirring continuously, until it becomes highly fragrant and deepens slightly in color.

Return the seared beef to the pot. Pour in the full-fat coconut milk, then add the bruised lemongrass stalks, kaffir lime leaves, cinnamon stick, brown sugar, and salt. Stir well to combine all the ingredients and bring the mixture to a gentle boil.

Reduce the heat to low, leave the pot uncovered, and let it simmer for 90 to 100 minutes. Stir occasionally to prevent sticking, watching as the coconut milk reduces, thickens, and eventually releases its oils.

Once the liquid has mostly evaporated, continue to fry the beef in the remaining spiced oil for an additional 10 minutes, stirring frequently until the meat is deeply caramelized and dark brown. Discard the lemongrass and cinnamon stick, then serve warm with freshly steamed jasmine rice.