BBQ flank steak with onions, mushrooms, tarragon and horseradish sauce

This chargrilled flank steak is served with smoky onions and mushrooms, then finished with a creamy tarragon and horseradish sauce. It’s a good barbecue main, but you could also cook it on a hot griddle pan. The combination of charred beef, sweet onions, earthy mushrooms and sharp, herb-flecked sauce makes this a simple but polished main for two.

This meal is protein-rich and built around vegetables, with the sauce adding some saturated fat but not overwhelming the dish. It’s a reasonably balanced barbecue-style main, especially if served with plenty of vegetables on the side.

Estimated nutrition (per serving, 2): kcal ~430–520, fat ~24–32g, saturated fat ~10–14g, carbs ~8–12g, sugars ~4–6g, fibre ~2–4g, protein ~34–40g.

Ingredients

For the BBQ flank steak, onions and mushrooms

• 2 red onions, cut into thick rings.
• 1 portobello mushroom, sliced.
• 4 oyster mushrooms, cut in half.
• 1 tsp chopped thyme leaves.
• 1 garlic clove, crushed.
• 250g/9oz flank steak.
• Olive oil, for drizzling.
• Salt and freshly ground black pepper.

For the tarragon and horseradish sauce

• 45g/1½oz unsalted butter.
• 1 banana shallot, finely chopped.
• 1 garlic clove, finely chopped.
• 100ml/3½fl oz white wine.
• 50ml/2fl oz white wine vinegar.
• 150ml/5fl oz chicken stock.
• 100ml/3½fl oz double cream.
• 3 tbsp freshly grated horseradish.
• 1 tbsp chopped tarragon.

Method

1. Preheat a griddle pan until hot.
2. Season the onions and mushrooms with salt and pepper, then chargrill them for 5–8 minutes, turning regularly, until soft and cooked through.
3. Transfer the onions and mushrooms to a bowl. Add a drizzle of olive oil, the thyme and garlic, cover with foil and leave to steam while you cook the steak.
4. Season the steak with salt and pepper. Grill for 2 minutes on each side, or until cooked to your liking, then transfer to a board and rest for at least 5 minutes.
5. To make the sauce, melt the butter in a saucepan over a medium heat. Add the shallot and garlic and cook gently until softened.
6. Add the wine and simmer until reduced by half. Add the vinegar and simmer again, then add the chicken stock.
7. Add the cream and horseradish and bring to the boil. Stir in the tarragon, then taste and season with salt and pepper if needed.
8. Slice the steak thinly against the grain. Toss with the onions, mushrooms and any resting juices, removing the clove of garlic before serving.
9. Serve the steak, onions and mushrooms with the tarragon and horseradish sauce spooned around.

Serving notes

The steak benefits from a short rest so the juices stay in the meat. Thin slicing against the grain is important here because flank steak can be chewy if cut the wrong way. The sauce is best made while the steak rests, so everything comes together quickly at the end.

Ingredient detail

The mushrooms and onions give this dish sweetness and depth, while the horseradish sauce cuts through with sharpness. Tarragon adds a light anise-like note that keeps the sauce from feeling too heavy. It’s a straightforward recipe, but the contrast of char, cream and herbs makes it feel restaurant-like.