Gnocchi with Tomato Sauce and Mozzarella

Heat olive oil in a saucepan over medium heat; cook onion until soft and translucent, about 5 minutes. Add passata and salt; simmer over low heat while you prepare the gnocchi.

Bring a large pot of lightly salted water to a boil. Cook gnocchi in the boiling water until they float to the top, 2 to 4 minutes. Drain.

Set an oven rack about 6 inches from the heat source and preheat the oven's broiler.