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Mushroom and Caramelised Onion Potato Crust Quiche

A potato rosti style crust takes this mushroom and caramelised onion quiche to the next level. This is both conveniently vegetarian and gluten free too, while also being healthier than your usual pastry crust!
Prep Time30 mins
Cook Time1 hr
Total Time1 hr 30 mins
Course: Lunch, Mains
Cuisine: American, Australian, French
Keyword: caramelised onion, flourless quiche, mushroom, potato crust, quiche
Servings: 6 people
Calories: 408kcal


  • 23cm / 9" Pie Dish (ideally without a removable base- see note 1)
  • Box Grater or Food Processor
  • Knife and Cutting Board
  • A Large Mixing Bowl
  • Colander or large sieve
  • Measuring Jug or a small Mixing Bowl


Potato Crust

  • 500 g / 1.1 lb potato use a starchy variety such as russet or sebago / approx. 3 large potatoes
  • 2 tbsp / 28 g unsalted butter melted
  • 1 tsp salt
  • cooking oil spray

Mushroom and Caramelised Onion Filling

  • 50 g / 3½ tbsp butter
  • 2 onions thinly sliced
  • 3 garlic cloves minced
  • 500 g / 1.1 lb mushrooms sliced
  • 1/2 tbsp dried thyme leaves

Egg and Cream Filling Mixture

  • 2 eggs
  • 1 cup / 250 ml thickened cream
  • 50 g parmesan cheese grated
  • 1 tsp salt
  • 1 tbsp black pepper


Potato Crust

  • Preheat your oven to 220°C/425°F (200°C/390°F fan) and spray your pie dish with a light coating of oil spray.
  • Wash, peel and grate the potatoes. I use a box grater (with the largest holes) as I find it fairly fast and less clean up than my food processor, but feel free to use the latter if you prefer. Rinse the grated potatoes in the colander under running water for a few minutes to remove excess starch.
  • Squeeze excess water out of potatoes by taking a handful at a time and squeezing between your hands over the sink. Make sure to get as much water out as possible. Then place this into a large mixing bowl and repeat with the rest.
  • Combine the melted butter and salt with the squeezed grated potato and mix.
  • Pour potato mixture into a prepared pie dish and spread at the base and up the sides of the dish with a spoon, packing down firmly as you go.
  • Spray the crust with another light coating of oil spray before placing the dish into the oven and baking for 30 minutes, or until golden around the edges.

Mushroom and Caramelised Onion Filling

  • Melt butter in a large fry pan over medium-high heat before adding the sliced onions and minced garlic. Cook for approximately 15-20 minutes until onions are soft and caramelised. During this time you can be prepping your mushrooms and/or making your egg and cream filling as you only need to be stirring the onions every few minutes- allowing them to sit allows the caramelisation to happen faster (but be sure to still keep an eye on them!)
  • Add the sliced mushrooms and dried thyme. Cook until mushrooms are softened and most of the excess moisture has evaporated from the pan. Take the mixture off the heat and set aside.

Egg and Cream Filling Mixture

  • In a measuring jug (or small mixing bowl), whisk the eggs, cream and salt and pepper until combined.

Putting the Quiche Together

  • Spoon and spread the mushroom and onion mixture into the pie dish over the potato crust.
  • Pour the egg and cream mixture over the mushroom and onion mixture, then top the quiche with the grated parmesan cheese.
  • Place the quiche back into the oven and bake for 15-20 minutes until lightly golden and set firm in the centre.
  • Allow the quiche to cool for 5-10 minutes before serving (see note 2).


  1. Using a pie dish with a removable base may mean you get some leakage of filling out of it and into your oven- if you only have a removable base dish, cover the base with aluminium foil and sit it another baking tray
  2. It is much easier to make clean slices in the quiche when it is cold, so if you're making this ahead it may be easier to slice prior to reheating. 
  3. Storage Instructions: Store in the fridge for up to 3 days. Suitable to freeze.
  4. Reheating Instructions: Best reheated in the oven but individual slices can be reheated in the microwave
  5. Nutritional information is an estimation only and will depend on your individual ingredients