Take the meat out at least 2 hours before. Pound it with a meat tenderizer. Clean it well, then wrap the bacon around it and tie it to maintain its shape. Meanwhile, preheat the oven to 350°F and place the roasting pan with the chopped vegetables, herbs, and wine inside. This way, when we transfer the meat to the pan, it will already be hot.

In a cast iron skillet, add the butter and oil, and once the butter is melted, add the meat. Sear the meat on all sides over high heat and season with pepper. Then take the pan with the vegetables from the oven and add the meat along with the liquid left in the skillet (do not clean the skillet as it will be used later). Cook in the oven at 350°F for about 30 minutes (it should remain pink inside). Baste frequently with its own juices, turning it on all sides.

Wrap it in aluminum foil and let it rest for 15-20 minutes. Then let it cool before slicing it into 1/4 inch thick slices. Strain the liquid and put it in the skillet where you seared the roast (there's the caramelized part). Salt if necessary and add a teaspoon of brown sugar if it tastes acidic from the wine, then reduce slightly.

Slice the onions. In a saucepan, add the butter and oil, and once the butter is melted, add the onions. Salt, pepper, and cook until they are golden. At this point, add the sugar and vinegar. Stir gently, raising the heat to evaporate the alcohol from the vinegar. Then lower the heat and slowly caramelize the onions.