Remove the foie gras from refrigeration and let sit at cool room temperature for 10 minutes. Using a sharp knife, portion the lobes into 4 equal rounds (about 4 oz / 115 g each). If there are visible veins, gently remove them with the tip of the knife; avoid overhandling to keep the lobes intact.

Season and dry

Pat each portion dry with paper towels. Lightly season both sides with kosher salt and freshly ground black pepper. If you prefer a light crust, dust each piece with a very light coating (about 1/4 tsp) of flour, tapping off any excess.

Cooking

Preheat pan

Place a heavy skillet (preferably stainless steel or cast iron) over medium-high heat. Add the neutral oil and allow it to heat until shimmering but not smoking (about 1–2 minutes).

Sear foie gras

Carefully place the foie gras rounds in the hot pan, flat side down, leaving space between them. Sear without moving for 30–45 seconds, until a deep golden-brown crust forms. Flip and sear the second side for 20–30 seconds. The internal temperature should be around 110–120°F (43–49°C) for rare, or 125°F (52°C) if you prefer slightly firmer; do not overcook—foie gras renders quickly.

Finish with butter and vinegar

Reduce heat to medium-low and add the unsalted butter to the pan. As it melts, tilt the pan slightly and spoon the foamy butter over the foie gras for 10–15 seconds to glaze. Remove the pan from heat, add the sherry vinegar to deglaze, swirl to combine and spoon a small amount over each piece. If using demi-glace, warm it separately and spoon a small spoonful onto each plate as a base.

Rest briefly

Transfer the seared foie gras to a warm plate and let rest 1–2 minutes. This brief rest allows the surface to set while retaining a silky interior.

Plating

Place a small smear or pool of demi-glace (if using) on each plate. Arrange toasted brioche slices beside or beneath each foie gras portion. Set the seared foie gras on the brioche, spoon a little of the pan glaze (butter + vinegar) over the top, and dot with fig jam or a small spoon of caramelized shallots if desired. Garnish with microgreens or frisée and serve immediately.