Cook the spaghettini in salted water according to the instructions on the package, making it firm to the bite. Depending on the manufacturer, this takes 1 - 2 minutes to drain and collect some pasta water.
Wash the fennel and cut in half. Cut out the stalk in a wedge shape. Peel down the hard fibers from the outer layers with a vegetable peeler. Cut the garlic into slices.
Heat the olive oil in a large saucepan or pan. First sweat the fennel in it until translucent, then add the garlic and sweat briefly. Add the prawns and let them turn pink for a moment. However, they should still remain relatively raw, as they will still follow and otherwise become too dry.
Deglaze with a good dash of white wine and season directly with salt, pepper and, depending on your taste, a pinch of sugar. Bring to the boil briefly, then stir in the pasta and some of the pasta water and let it steep briefly so that the pasta can absorb the taste.
If you want and have it ready to hand, refine with 1 - 2 teaspoons of basil pesto. Sprinkle with parmesan and serve with a light white wine.
The quantities given for pasta and prawns are estimates and are based on the chef`s taste.