In a large nonstick or cast-iron skillet, heat the olive oil over medium heat.
Add garlic and red pepper flakes. Sauté for about 30 seconds, just until fragrant.
Stir in the tomato paste and let it toast for 1-2 minutes.
Pour in the tomato purée and sugar, if using. Cook for 3-4 minutes to deepen the flavor.
Add the uncooked spaghetti directly to the skillet. Pour in about 1 cup of water, enough to cover the bottom of the pan.
Let the pasta sit undisturbed until the water is absorbed and a crispy layer forms underneath.
Flip or stir gently to avoid breaking the pasta. Add more water gradually, allowing it to absorb each time.
Repeat until the pasta is cooked through but crisp in spots. Total time about 15–18 minutes.
Serve hot with fresh basil, if desired.