Start by placing a skillet over medium heat. Add the finely-diced shallots and a touch of olive oil. Sauté until they turn translucent and fragrant, which will take about 2-3 minutes. This step lays the foundation for a complex flavor profile. Shallots add subtle sweetness that balances out the saltiness from other ingredients.

Next, it’s time to deglaze! Pour the firm dry red wine into the skillet. Scrape down the sides of the pan to lift any flavorful bits stuck to the bottom. Allow the mixture to simmer for about 5 minutes. This will reduce the wine and concentrate the flavors, leading to a robust foundation for your sauce.

Once the wine has reduced, add in the aged balsamic vinegar and demi-glace. Stir well to combine. Let this simmer for another 3-4 minutes. The combination of the demi-glace with balsamic will create a luscious sauce texture with rich, layered flavors.

After the mixture simmers, add a pinch of sea salt and freshly cracked black pepper to taste. Now, slowly whisk in the unsalted butter, which will emulsify and make the sauce creamy. This is the magic moment! Keep stirring until the butter is fully incorporated and the sauce becomes silky smooth.

Now comes the pièce de résistance! Gently fold in your shaved black truffles. Be sure to reserve a few slices for garnishing later. Allow the sauce to sit off heat for just a minute. This will let the truffle aroma permeate the sauce without losing its delicate flavor.