Bring a large pot of water to the boil. Add the tortellini and cook for the length of time indicated on the package. In my case it was 12 minutes. When cooked, drain.
Meanwhile, heat 1 tablespoon of the oil from the jar of sun-dried tomatoes in a large pot over medium heat. Fry the onions until soft and transparent then add the garlic and fry for a minute or so more until soft and transparent.
Add the tomato paste and stir well. Fry for a couple of minutes, stirring frequently to prevent burning, until the tomato paste has darkened slightly in colour.
Add the sun-dried tomatoes, vegetable stock and can of crushed tomatoes. Bring to a boil then reduce to a gentle simmer and simmer for 10 minutes.
Remove from the heat and blend with an immersion blender or carefully transfer to a blender and blend, with the lid ajar to allow steam to escape, until smooth.
Blend in the coconut milk. If you're worried you might be able to taste it, add it a quarter cup at a time, tasting as you go, until you're happy with the creaminess. Taste and add salt. If you find it a bit sour, add the sugar. If you'd like it thinner, add another splash of stock.
Add the cooked tortellini and garnish with chopped basil, if desired.