Portobello Steak Diane

Portobello Steak Diane
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My partner and I do an at-home steak house night for Valentine’s Day every year. This tradition was born after a less-than-favorable experience at a very expensive steak house. The following year, we decided to take the steak house menu into our own hands and have never looked back. Steakhouse classics are, after all, fairly simple to make. And no matter how expensive a ribeye is in the grocery store, it’s guaranteed to be cheaper than any steak you’d order off a menu. Each year we tinker with these classics and come up with fun alternatives. These dishes maintain the spirit of the traditional chop house but are unique to us and our tastes. Today’s Portobello Steak Diane is our first plant-forward riff and I am head-over-heels in love with it.

Portobello mushrooms in a large bowl.

Steak Diane is a classic steak dish that features a seared steak dressed in a cognac and cream pan sauce accented with tomato paste, mustard, and Worcestershire sauce. It resembles the French classic Steak au Poivre, but Steak Diane is not French. An Englishman named Tony Clerici claimed he invented it at his London restaurant Tony’s Grill in 1938. According to him, the dish was named in honor of Lady Diana Cooper. But enough about Steak Diane, let’s make Portobello Steak Diane!

The mushroom marinade in a glass bowl ready to be whisked.

We’re going to kick things off by making a marinade for our portobello mushrooms. Place olive oil, soy sauce, Dijon mustard, lemon juice, and a minced clove of garlic in a bowl. Add fresh ground pepper and whisk to combine. Place the mushrooms in a wide, shallow vessel or a freezer bag. Pour the marinade over the mushrooms and toss to coat. Transfer the mushrooms to the fridge and marinate for 30 minutes to an hour.

Pouring the marinade over the portobello mushrooms.

While the mushrooms are marinating, preheat the oven to 400°F. Once the mushrooms are good to go, heat some neutral oil in a large cast iron skillet. Add your mushrooms to the now-smoking skillet and sear them on both sides. This is more for appearance and for building up some extra fond to work with later.

Searing the portobello mushrooms in a large cast iron skillet.

Once the mushrooms are seared on both sides, transfer the skillet to the oven. Roast the mushrooms for 15 minutes before flipping them. Return the mushrooms to the oven and roast for 15 minutes more. The finished mushrooms should be quite tender. Transfer the mushrooms to a plate and keep them warm while you work on the pan sauce.

Adding cream to the steak Diane sauce.

Now, the most important piece of advice I can give you for making this pan sauce is not to grab the skillet’s handle. I have done this so many times with so many different dishes and it sucks. Remember the pan was in a 400°F oven for 30 minutes. So this is not your typical stovetop preparation. I recommend placing a tea towel on the handle of the frying pan to remind you not to grab it willy-nilly. There is seriously nothing worse than a burn on the palm of your hand. 

Portobello Steak Diane

Start by adding a couple of diced shallots to the pan. Keep the heat relatively low. The residual heat of the pan will be enough to soften and melt the shallots. Once the shallots are translucent, stir in some cognac to deglaze the pan. Simmer until the cognac is reduced by half. Pour in some veggie stock and add tomato paste, Dijon mustard, and Worcestershire sauce or soy sauce. I’m giving you an alternative because Worcestershire is technically not vegetarian. It contains anchovies. So if you are strictly vegetarian or vegan or you’re making this for somebody who is, use either a vegan Worcestershire sauce or failing that soy sauce. I know vegan Worcestershire can be difficult to track down.

Portobello Steak Diane

Stir everything together and bring the mixture up to a spirited simmer. Once again, simmer until the sauce is reduced by half. You can tell your sauce has thickened when the bubbles on the surface of the sauce build and break at a slower and lazier pace. Pour in the cream and simmer for another 2-3 minutes or until thickened. Finish the sauce with a couple of pats of butter (dairy or plant-based) and stir until the butter has melted.

Portobello Steak Diane

From here, it’s as simple as plating everything up. Place two portobello steaks on a plate and spoon the sauce over top. Finish with a sprinkling of finely chopped chives and serve immediately. I like to serve this dish with mashed potatoes, so make sure you save a little of that pan sauce for those. You can thank me later.

That’s everything you need to know about this Portobello Steak Diane. A plant-forward version of the 1930s British bistro classic.


Portobello Steak Diane

Portobello Steak Diane

This Portobello Steak Diane is a veggie-forward riff on the classic steak dish. It features marinated portobello mushrooms seared and roasted to perfection dressed in a rich cognac and cream pan sauce.
Prep Time 15 minutes
Cook Time 40 minutes
Marinating Time 30 minutes
Course Main Course
Cuisine British
Servings 2


  • 1 Large Cast Iron Skillet


  • ¼ cup olive oil
  • ¼ cup soy sauce
  • 2 cloves garlic minced
  • 2 tbsp Dijon mustard divided
  • ½ lemon juiced
  • Fresh ground pepper
  • 4 portobello mushrooms
  • 1 tbsp neutral oil I used canola
  • 2 shallots diced
  • ¼ cup cognac
  • ½ cup vegetable stock
  • 1 tbsp tomato paste heaping
  • 1 tbsp Worcestershire sauce or soy sauce **
  • cup heavy cream
  • 2 tbsp butter
  • ¼ cup chives finely chopped


  • Pour olive oil and soy sauce into a small bowl. Add the garlic, Dijon mustard, lemon juice, and fresh ground pepper. Whisk to combine.
    ¼ cup olive oil, ¼ cup soy sauce, 2 cloves garlic, 2 tbsp Dijon mustard, ½ lemon, Fresh ground pepper
  • Place the mushrooms in a freezer bag or a large shallow dish. Pour the soy sauce mixture over top and toss to coat. Transfer the mushrooms to the fridge and marinate for 30 minutes.
    4 portobello mushrooms
  • Preheat the oven to 400°F. Heat neutral oil in a large cast iron skillet over medium-high heat. Once the oil is shimmering, add the mushrooms to the pan. Sear the mushrooms on both sides. Transfer the pan to the oven and roast for 15 minutes. Flip the mushrooms and roast for 15 minutes more.
    1 tbsp neutral oil
  • Take the skillet out of the oven and transfer the mushrooms to a plate and set them aside. Place the skillet over medium heat. Add the shallots and saute until softened.
    2 shallots
  • Deglaze the pan with the cognac and stir until reduced to half. Pour in the veggie stock and add the tomato paste, and Worcestershire or soy sauce. Simmer once again until reduced by half, this should take 2-3 minutes.
    ¼ cup cognac, ½ cup vegetable stock, 1 tbsp tomato paste, 1 tbsp Worcestershire sauce or soy sauce **
  • Add the cream to the skillet and simmer for another 2 minutes then add the butter. Stir until the butter melts. Take the sauce off of the heat.
    ⅓ cup heavy cream, 2 tbsp butter
  • Place two mushrooms on a plate and spoon the sauce over top. Repeat with the remaining mushrooms. Garnish with fresh chives and serve immediately.
    ¼ cup chives


** If you are vegetarian swap the Worcestershire sauce for vegan Worcestershire sauce. If you can’t find the vegan version, use soy sauce. It works in a pinch. 
Keyword chives, cognac, Cream, portobello mushrooms

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