Preheat the oven to 400°F (205°C). Put the flour in an oven-safe pan and spread it evenly. Cook in the oven, stirring every 15 or 20 minutes, for 1 ½ to 2 hours, or until the flour is the color of light brown sugar.
Melt 2 tablespoons (30 g) of the lard in a large pot over high heat. Once it’s sizzling, add in the beef and ham knuckle. Cook the meat for a few minutes, getting it nice and browned all over. Remove the meat and set aside.
Add the rest of the lard, and once it’s hot, whisk in the browned flour and cook for about 1 minute.
Add the meat back in along with the okra, onion, bell pepper, and salt. Reduce the heat to medium and cook, stirring frequently, for 20 minutes.
Stir in the hot water, scraping up the browned bits from the bottom of the pot. Bring it to a low boil and cook uncovered for 2 hours, stirring frequently.
After 2 hours, taste and add salt if desired. Add in the shrimp and crab, then cook for another 5 to 7 minutes, or until the shrimp have curled up and become opaque.
Serve the gumbo forth with Carolina rice.
