1. Preheat the oven to 200°C (400°F).
2. Melt butter in a large saucepan over medium-high heat. Add mushrooms and fry, without stirring too often. Cook until nicely coloured, about 7 to 8 minutes.
3. Add the potatoes and broth and cook until potatoes are tender and have absorbed all the broth, about 15 minutes. If potatoes are still too hard, add more broth.
4. Add the cream and stir gently. The potatoes will absorb the cream.
5. Add the Parmesan and thyme, and then place under the broiler for 5 minutes to melt the cheese.
6. Serve. 

Chef’s secret

For thin slices of potato, cut it using a mandolin.
By not stirring the mushrooms too much, we produce less liquid resulting in nicely coloured mushrooms.