French onion soup root vegetable gratin

Humble vegetables get all dressed up!

Confession time: I’ve never been a big fan of rutabagas (the proper name for yellow-fleshed turnips). I love the little white turnips but haven’t found too many ways to use rutabagas…until now. Working with a bountiful crop of root vegetables in my recent Farmhouse Food Harvest Box inspired me to think about some new ways to enjoy local late fall and winter produce; this recipe is a result of some concerted brainstorming. I’ve often made vegetable gratins with a cream sauce, but this French onion soup version is so much more flavourful. I loved the looks of surprise and delight on my guests’ faces when they took their first bites. If you like this dish, you may also enjoy my French onion soup pasta casserole.


  • 2 tablespoons (30 mL) olive oil
  • 3 large yellow onions, thinly sliced (about 4 cups / 1 L of sliced onion)
  • 3 tablespoons (10 mL) flour
  • 3 cups (750 mL) beef broth
  • 1 tablespoon (15 mL) brandy or white wine
  • 1 teaspoon (5 mL) Dijon mustard
  • 1/2 teaspoon (2.5 mL) dried thyme leaves
  • Kosher salt and freshly ground pepper, to taste
  • 6 cups thinly peeled and thinly sliced root vegetables (I used 1/2 a rutabaga, 2 white beets, 2 medium sized potatoes and 2 carrots)
  • 1 cup (250 mL) grated Tomme or Swiss cheese, divided
  • 1 cup (250 mL) grated mozzarella
  • 1/2 cup (125 mL) panko or other dry bread crumbs


  • In a large, heavy saucepan, melt butter over medium heat.
  • Add onions and pinch of salt.
  • Cover pan and sauté until onions are very soft, stirring occasionally, about 20 minutes. To caramelize the onions, remove the pan’s lid and increase heat to medium-high; cook, stirring often, until onions take on a golden brown hue without burning (an additional 10 – 15 minutes).
  • While onions are cooking, peel, slice and par-cook the root vegetables. Put them all in a large pot of water and add 1 teaspoon (5 mL) of salt. Bring to a boil and cook over medium heat until just tender, about 5 minutes. Drain immediately.
  • Turn oven on to 350F to preheat.
  • Once onions are caramelized, add flour and continue to cook, stirring constantly, for 2 minutes.
  • Add beef broth, brandy or wine, mustard and thyme. Stir to blend well then season to taste with salt and pepper.
  • Stir in 1/2 cup (125 mL) of the Tomme or Swiss cheese.
  • Combine remaining Tomme or Swiss cheese, mozzarella and panko in a small bowl.
  • Coat the bottom of a 9 x 12 inch (22.5 x 30 cm) casserole dish with a few spoonsful of the French onion soup mixture. Add half the parboiled vegetables, spreading out in an even layer.
  • Top with half of the remaining French onion soup mixture, followed by the rest of the vegetables in an even layer and the remaining soup mixture. Sprinkle cheese and panko mixture evenly over top.
  • Note: the dish can be prepared ahead of time to this point; if not cooking within the hour, cover and refrigerate for up to 24 hours.
  • Bake in preheated oven for 30 – 40 minutes, until bubbling and golden brown on top. Serve hot.

Serves 6.


Author: Paula Roy

Welcome to my kitchen! I love simple dishes prepared with passion and am always seeking to find new methods to make food as fun and flavourful as possible. If you enjoy this space be sure to check out my Rogers TV Ottawa cooking show, Paula Roy's Favourite Foods, available on local cable, streaming and a dedicated playlist on Rogers TV's YouTube channel.

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