Place a pan on the stove on medium low. Add the cubed salt pork and cook, very slowly, for 45-60 minutes until rendered, brown, and crispy. Strain the fat, making sure to save it, and drain the cubed bits on paper towl.
In the same pan, add back 2 tbsp of the pork fat on medium heat. Add the thyme leaves and chili flake (if using). Fry for a quick 30 seconds, then add the Brussels sprouts and sauté for 10-15 minutes, stirring frequently, until cooked through but not mushy. Season with salt to taste and serve, tossed with the cubed pork bits.