Heat 4 tbsp of the olive oil and the butter in a large pan. Add the sliced onion and a pinch of salt and cook gently for a few minutes.
Add the thyme and garlic and cook for about 30-40 minutes, stirring occasionally, until you have lovely caramelised onions.
Meanwhile, put the tomatoes in a roasting tin, drizzle with the final 1tbsp of the oil and season. Roast for 25-30 minutes at 200°C (180° Fan).
Once the onion is cooked, scoop out of the pan and then return the pan to a medium high heat and cook the pancetta for 5-6 minutes until golden.
Cook the pasta in boiling salted water for 5 minutes.
Return the caramelised onion to the pan and add the roasted cherry tomatoes and diced brie.
Remove the pasta with tongs and add straight to the frying pan, keeping the pan over a low heat. Toss to combine, letting the heat melt the brie. Serve Straight away.
Notes
The marriage of brie, caramelised onion and pancetta here is a serious winner. If you're thinkin' comfort food, this is the one.