Now add the fusilli along with the boiling water. The sauce will be very watery and runny but don't worry- the pasta will absorb all the excess water as it cooks.
500 g dried fusilli, 950 ml boiling water
Bring to the boil, and then simmer for 10 to 12 minutes, stirring often, until the pasta has cooked and the sauce has thickened back up. If it goes too dry, add some more water. It's hard to say how much you'll need because some pasta brands are thicker than others.
Now add the spinach, basil and butter, and stir over a low heat until it's cooked down.
A few handfuls of fresh basil, 250 g fresh spinach, 30 g butter
Finally, stir in the mascarpone until melted. You should have a deliciously thick, creamy sauce.
3 heaping spoonfuls of mascarpone
Serve immediately.
Notes
If you want to use vegetable stock instead of water, you can omit the salt.