Clean and finely slice the mushrooms. Finely chop the onion.
Heat a large pan over medium heat. Once hot, add butter and allow to melt. Once the butter has melted and is hot, add onion and sauté until onion is translucent (4-5 minutes). Add garlic and cook for another minute.
Add lemon juice, thyme, salt, pepper and sliced mushrooms. Fry for a few minutes until the mushrooms start to release their juices.
Add cauliflower and stir to coat with the melted butter. Add the white wine and stir until it has mostly evaporated.
Turn the heat down to low. Add the vegetable broth 1/4 cup at a time while stirring. Allow most of the vegetable broth to bubble away before adding the next 1/4 cup.
Once the last bit of broth has been added, stir in the cream.
Cover the pan and cook for a further 3 - 5 minutes till the cauliflower has steamed through and is tender.
Remove from the heat and add the parmesan cheese. Mix well and serve. Garnish with more parmesan cheese if desired.