Cook the spaghetti in a large bowl with one-liter boiling water and half a teaspoon of salt until al dente. This takes about 9-12 minutes -> Have a look at the label of the spaghetti package to know the exact time.
Meanwhile, peel the garlic cloves and onion and cut them into thin slices.
Preheat a nonstick frying pan with two tablespoon olive oil and roast the sliced garlic and onion for 3 minutes over medium heat.
Cut the tomatoes into small cubes and add them to the pan. Cook for another 1 minute, then add a half tablespoon of sugar and caramelize it for 2 minutes.
Add the water and creme fraiche to the pan and cook until the spaghetti is al dente. Season it with salt and pepper.
When your spaghetti is al dente, drain them and add them to the sauce.
Cook the spaghetti with the sauce together for another minute, this helps that the sauce will stick on the spaghetti.
Notes
I always keep a bit of the pasta water left when I drain them so that I can add a bit of it to my sauce when it gets too dry. Serve your spaghetti with some parmesan.