Set a large saucepan over a medium heat, add in the oil & butter, leave to melt then add in the diced onion & a pinch of salt.
Cook the onion for 5-10 minutes, stirring frequently until soft then stir in the garlic & thyme and cook for another minute.
Next, stir the rice into the onions, cook for a minute then pour in the wine. Keep cooking for another 2-3 minutes, until the wine has reduced almost completely.
Turn the heat down to low then stir 2 ladles of warm stock into the risotto. Keep stirring, until the rice has absorbed all the stock then add in another 2 ladles of stock.
Repeat this process until all the stock has been used & the rice is just cooked al dente. This will take roughly half an hour. Once cooked, the risotto should be fairly thick but will thin out once we add the butternut puree in. Next, stir the butternut squash puree into the risotto then cook for another 3-4 minutes, until the risotto is thick & creamy.
Add the grated parmesan & the lemon juice into the risotto, stir to melt then season to taste with sea salt & freshly cracked black pepper.
Take the risotto off the heat, cover with a lid & leave to rest for 5 minutes, whilst you make the brown butter.