Portobello French Dip with Horseradish Aioli

Portobello french dip on a roll with caramelized onions.

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It’s hard to describe how much there is to love about these sandwiches, but I’ll try:

Crunchy, buttery, toasted bread is going to meet up with roasted steak-seasoned portobello strips, sweet and golden caramelized onions, a sheet of melted Provolone, and a big thick smear of horseradish aioli…

And then just when you think it can’t even get any better, that whole beautiful crispy, saucy, golden sandwich gets dunked in a richly savory, no-meat-necessary, au jus dipping sauce.

Ingredients for portobello french dip.

It is wonderful, it is meatless, it is the epitome of comfort food.

Dipping portobello french dip into au jus.

Watch How To Make This Recipe:

French dips are a type of sandwich that normally contain beef, onions, and cheese (also called beef dips) and their trademark is that they get dipped in an au jus (brothy kind of sauce). According to this nice little history of French dips, they are an American invention, but they’re called French due to the type of bread usually used.

Common Questions About French Dips

What can I substitute for Worcestershire sauce?

You can use vegan Worcestershire sauce or substitute soy sauce.

What can I use instead of white wine?

You could add a little bit of water instead.

How can I make this gluten-free?

We’d suggest using gluten-free Worcestershire sauce, tamari or coconut aminos in place of soy sauce, and using a gluten-free baguette or roll.

A picture of Portobello French Dip with Horseradish Aioli

Portobello French Dip with Horseradish Aioli

  • Author: Lindsay
  • Total Time: 45 minutes
  • Yield: 4 mega sandwiches


These Portobello French Dips are about to change your life! Roasty portobello strips, golden caramelized onions, melted Provolone cheese, zippy horseradish aioli, all piled on a warm, crusty roll.


Roasted Mushrooms

  • 4 portobello mushroom caps, sliced into thin strips
  • 23 tablespoons olive oil
  • 12 teaspoons Montreal steak seasoning (or just a sprinkle of salt and pepper)

Caramelized Onions and Au Jus

  • 2 tablespoons butter
  • 1 large onion, thinly sliced
  • 1/4 cup white wine
  • 1 tablespoon Worcestershire (omit for vegetarian / vegan)
  • 1 tablespoon soy sauce 
  • 2 cups beef or vegetable broth
  • salt, pepper, and a pinch of sugar to taste

Horseradish Aioli

  • 1/2 cup mayo
  • 1 teaspoon horseradish
  • 1 clove garlic, grated
  • pinch of salt

French Dip Essentials

  • 4 crusty sourdough rolls, or a baguette cut into 4 sections 
  • Provolone cheese slices


  1. Roast the Mushrooms: Preheat oven to 450 degrees. Toss mushroom slices with oil and seasoning. Roast for 20-30 minutes. 
  2. Caramelize the Onions: Meanwhile, melt the butter in a large skillet over medium heat. Add onions; saute until softened, then turn the heat down to caramelize the onions for 20 minutes or so, stirring occasionally until they are deep golden brown.
  3. Make the Au Jus: Add the wine to the onions in the pan. Let it sizzle out. Add the Worcestershire and soy sauce. Add the broth. Simmer until reduced slightly. Pull out the onions with tongs and set aside. Season the au jus to taste.
  4. Toast the French Dips: Butter the bread if you want. Pile mushrooms on the bread. Cover with cheese. Return to the oven on the same roasting pan for about 5 minutes (enough to toast the bread and melt the cheese). 
  5. Feast: Top the sandwiches with caramelized onions. Give em each a dollop of horseradish aioli. Serve with the au jus for dipping! HOLY MOLY that’s good.


  • Prep Time: 15 minutes
  • Cook Time: 30 minutes
  • Category: Sandwich
  • Method: Oven
  • Cuisine: American

Keywords: portobello mushrooms, french dip, vegetarian sandwich, caramelized onions

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This recipe is part of our collection of delicious mushroom recipes. Check it out!

The post Portobello French Dip with Horseradish Aioli appeared first on Pinch of Yum.

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