About 3.5 oz of tenderloin per guest (or more)
2 large onions
1 cup red or white wine (optional)
Extra virgin olive oil
First we are going to caramelize the onions. It can be done in the traditional way, which is undoubtedly the best, or take a shortcut to significantly reduce the cooking time. If we do the traditional method we will take the onion and cut it into strips. We'll put in a small clay pot with olive oil to cover it and we'll put the low heat stirring every ten minutes. With the slow heat the sugar of the same onion goes out and turns its color to a very dark purple almost black. Only near the end of the process add a pinch of salt. The problem is that to get a complete browning can take as long as we want as it depends on firepower, but 4, 6 and 12 hours could be gastronomically logical. As we do not usually have as much time there is another way that produces acceptable results. Cut the onion into strips also and we cover just with virgin olive oil. Incorporate a couple of lumps of brown sugar to dissolve in half a glass of red wine or white wine. Stir constantly over medium heat and in half an hour the onions are caramelized.
If we did a good caramelized onion is compact whole, only very obscured. For this particular recipe is our interest that does not get too brown, so remove it when it is still a bit white. This may mean something less than twenty minutes of the rapid method.
Meanwhile cut the tenderloin into medallions and season, sprinkle with chopped parsley. Then fry slowly in a clay pot until only the heart is pink. Pour onions to be baked with the meat juices. Therefore we do not incorporate all the oil, just the half. Preheat oven to 356 F and cook until the onion becomes dark tone desired. 20 minutes should be enough.
The dish is visually very strong, and the contrast between sweet onion and sirloin provides a very pleasant feeling. You have to constantly watch the final stage of baking as it is very easy to burn the onion before reaching the desired point. Do not suffer about the meat, cause tenderloin is very soft, just watch the onion. Too much oven can spoil the recipe.