Allow the pork lard to melt in a saucepan over medium heat then add the onion. Sauté until golden and soft.
Next, stir in the tomato sauce and cook for a minute. Then, add the flour and stir vigorously to incorporate the flour into the sauce. Once incorporated, start pouring in the beef stock, little by little, whisking constantly until you get a creamy sauce that isn't too watery.
Add the peppercorns, allspice, vinegar and sugar and simmer the sauce for 15-20 minutes until thickened. Adjust the seasoning after this if needed.
Take the sauce off the heat. If you prefer a smoother texture, you can use a immersion mixer to break apart the onion and any other remaining clumps in the sauce.
Pass the sauce through a strainer into a separate dish, add the butter and stir until it melts into the sauce.
Serve the cooked beef with a generous amount of sauce and pair with some dumplings as a side dish!
Enjoy!