Preheat the oven to 400°F (200°C)
Cut any bigger tomatoes into halves or quarters.
Arrange the tomatoes and onion wedges in a small roasting dish so they fit quite snugly together.
Scatter the anchovies and garlic over the top, then sprinkle over the red pepper flakes and drizzle with the honey and olive oil. Season well with salt and pepper.
I tend to leave skins on garlic cloves then squeeze them out after roasting but peel them first if you prefer.
Roast for 45 minutes to 1 hour, or until the onions and tomatoes are lightly charred around the edges.
Transfer everything to a saucepan and blend until smooth with a stick blender. Alternatively, blend in a food processor.
Add the cooked pasta straight into the sauce with a splash of pasta water and the butter, if using.
Let the pasta gently bubble in the sauce for 1–2 minutes, then divide between plates and top with freshly grated parmesan, the torn basil leaves and a drizzle of olive oil.