In a bowl, mix the tomato passata, tomato paste, and 1/2 cup hot water. Set aside.
In a large non-stick or cast iron skillet, heat olive oil over medium heat. Add the garlic and red pepper flakes, cooking for 1-2 minutes.
Add the dry spaghetti in a single layer and let it toast for 2-3 minutes per side until golden and slightly charred.
Pour in the tomato mixture and season with salt. Let the pasta absorb the sauce as it cooks.
Gradually add the remaining hot water, about 2 tablespoons at a time, only when the pan is dry. Do not stir constantly; flip the pasta occasionally to char evenly.
Cook until the pasta is al dente and has absorbed most of the sauce, with slightly crispy edges.