In a heavy-bottomed Dutch oven, melt Duck Fat over medium heat.
Add Ground Beef and Yellow Onion and cook, breaking up the beef with a spoon, until browned, about 10-12 minutes.
Add Tomato Paste, Ancho Chili Powder, Smoked Paprika, Cayenne Pepper, and Garlic. Cook for 2 minutes, stirring constantly.
Pour in Beef Stock and Red Wine Vinegar. Bring to a simmer, then reduce heat to low, cover, and cook for 60-75 minutes, stirring occasionally, until the sauce is rich and deeply flavored.
Stir in grated Dark Chocolate and season with Sea Salt and Freshly Ground Black Pepper to taste.
Toast Potato Rolls with butter.
Place a Hot Dog in each toasted roll and top generously with the meat sauce.
Garnish with Stone-Ground Mustard and Pickled Red Onions.
