Balsamic Beef Recipe

Prepare steak

Trim any excess fat from the flank steak. If the steak is very thick (over 1 inch), slice it horizontally to about 3/4–1/2-inch thickness for more even marinating and cooking.

Make marinade

In a medium bowl, whisk together 3 tablespoons extra-virgin olive oil, 4 tablespoons balsamic vinegar, 2 tablespoons soy sauce, 1 tablespoon Dijon mustard, 1 tablespoon brown sugar, 3 minced garlic cloves, 1 teaspoon kosher salt, 1 teaspoon freshly ground black pepper, and 1/4 teaspoon red pepper flakes (if using). Stir in 1/2 cup thinly sliced fresh basil.

Marinate

Place the steak in a large resealable plastic bag or shallow dish. Pour the marinade over the steak, pressing out excess air from the bag and ensuring the steak is well coated. Seal and refrigerate for at least 2 hours and up to 8 hours (overnight is fine but no more than 12 hours to avoid over-tenderizing). Turn the bag or flip the steak once halfway through marinating.

Bring to room temperature

About 30 minutes before cooking, remove the steak from the refrigerator and let it sit, sealed, at room temperature. Reserve the marinade for finishing (see next steps).

Preheat and prepare

Heat a heavy skillet (cast iron preferred) or grill to medium-high heat. Pat the steak dry on both sides with paper towels — this promotes a good sear. Lightly brush or rub the steak with the remaining 1 tablespoon olive oil if needed and sprinkle a little extra salt and pepper on both sides.

Sear the steak

Place the steak in the hot skillet or on the grill. Cook without moving until a deep brown crust forms, about 4–5 minutes per side for medium-rare for a 3/4–1-inch steak (internal temperature 125–130°F / 52–54°C). Adjust time for thickness and desired doneness. For medium, aim for 6–7 minutes per side (135°F / 57°C). Use an instant-read thermometer for accuracy.

Rest the steak

Transfer the steak to a cutting board and tent loosely with foil. Let rest 8–10 minutes; carryover cooking will raise the internal temperature a few degrees and juices will redistribute.

Reduce reserved marinade (optional finishing sauce)

While the steak rests, pour the reserved marinade into a small saucepan and bring to a boil over medium-high heat. Boil for 2–3 minutes, then reduce heat and simmer 3–4 minutes until slightly thickened and reduced by about one-third. Remove from heat and whisk in 1 tablespoon butter and 1/2 teaspoon lemon juice (optional) to round the flavor. Taste and adjust with a pinch of salt if needed. This step ensures the marinade is safe to serve since it contacted raw meat.

Slice and serve

Slice the steak thinly against the grain into 1/4-inch slices. Arrange on a platter or individual plates. Spoon a little of the warm reduced balsamic sauce over the sliced beef and scatter the torn fresh basil leaves over the top as garnish. Serve immediately.