A delicious creamy leek and mushroom bake, that is perfect for Thanksgiving, Christmas or for entertaining any time of year. It’s also easy enough for family dinners, too!

mushroom leek gruyere casserole in baking pan with spoon

This delicious and cream leek and mushroom bake is a bit different from the usual side dish. It’s easy to make and can be made ahead, as it re-heats quickly/ I also love that it has flavours that everyone will enjoy.

This mushroom side dish features sautèed leeks and a creamy sauce flavoured with a bit of grainy mustard and lemon juice. The lemon juice is the perfect touch of acidity that heightens the flavours and prevents this dish from becoming overly rich. On top, is a crispy topping made from fresh bread crumbs (just throw a couple of slices of bread in a food processor) and some Gruyere cheese. It doesn’t have a ton of cheese. Gruyere has loads of flavour, so a little goes a long way. It’s the perfect complement to the mushrooms.

Ingredients and Substitutions

Mushrooms – white button mushrooms or cremini mushrooms (or a combination of both) work well here.

Leeks – leeks benefit from a good washing after slicing and before cooking, as dirt often hides in the many layers.

Heavy Cream – this is aka whipping cream, which is 35% butterfat cream. Using a lighter cream will make a thinner sauce.

Recipe Tips

Be sure to taste and season the mushrooms with salt, to bring out all the great flavours.

Of course, it goes without saying that this dish would also be perfect any time of year – for entertaining, or next to simple grilled chicken, pork or beef for any meal at home. It comes together quickly and is sure to become a family favourite.

mushroom leek gruyere casserole in baking pan with spoon

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creamy mushroom and leek bake in baking dish with spoon

Get the Recipe: Creamy Leek and Mushroom Bake

A delicious side dish of mushrooms and leeks with a creamy sauce, flavoured with mustard and lemon juice and topped with a crispy bread crumb and cheese topping. Can be made ahead!
5 stars from 2 ratings
Prep Time: 10 minutes
Cook Time: 40 minutes
Total Time: 50 minutes
Yield: 8 servings


  • 5 Tablespoons butter, divided
  • 1 stalk leek, (white and light green parts only), halved lengthwise and then sliced crosswise
  • 1/2 teaspoon each salt and pepper
  • 24 oz cremini and/or button mushrooms, sliced (three 8oz trays)
  • 1/3 cup all-purpose flour
  • 1 1/4 cups chicken broth, or sub vegetable broth to keep it vegetarian
  • 1/2 cup whipping cream 35%
  • 2 Tablespoons grainy Dijon mustard
  • 1/2 cup chopped fresh parsley
  • 1 Tablespoon chopped fresh thyme
  • 4 teaspoons lemon juice

Gruyère Crumb Topping:

  • 2 cups fresh bread crumbs, slightly stale bread, processed in food processor
  • 3/4 cup grated Gruyère cheese
  • 2 Tablespoons butter, melted
  • 2 Tablespoons chopped fresh parsley


  • In a large skillet, melt 1 Tbsp. of the butter over medium heat. Cook leeks and half each of the salt and pepper, stirring often, until leeks are softened, about 6 minutes. Remove to bowl and set aside.
  • In the same skillet, melt the remaining 3 Tbsp. butter over medium heat. Cook mushrooms with the remaining salt and pepper, stirring occasionally, until mushrooms are just tender and have released their juices, 5 to 8 minutes. Sprinkle with flour and cook, stirring, until light golden, about 2 minutes. Return the leeks to the pan.
  • Whisk in broth, cream and mustard until smooth. Cook, whisking, until thickened, 3 to 5 minutes. Stir in parsley, thyme and lemon juice. Spoon into shallow 8-cup casserole dish. (Make-ahead: Let mushrooms cool to room temperature, then cover and refrigerate for up to 24 hours. To reheat, cover with foil and bake in 375° F. oven until hot and bubbly, 40-50 minutes. Uncover and continue with recipe. You can also mix together the crumbs and cheese of the crumb topping and refrigerate ahead. When ready to broil, stir in parsley and melted butter.)
  • Gruyère Crumb Topping: In bowl, stir together bread crumbs, Gruyère cheese, butter and parsley. Sprinkle over mushroom mixture. Broil until topping is golden, 2 to 4 minutes.


Be sure to read the notes above this Recipe Card, for more tips on making this recipe.
Cuisine: American
Course: Side Dish
Serving: 1serving, Calories: 327kcal, Carbohydrates: 24g, Protein: 8g, Fat: 21g, Saturated Fat: 12g, Cholesterol: 61mg, Sodium: 513mg, Potassium: 125mg, Fiber: 1g, Sugar: 1g, Vitamin A: 745IU, Vitamin C: 6.5mg, Calcium: 198mg, Iron: 2mg
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