Bring a large pot of salted water to a boil. Cook the spaghetti until al dente according to package instructions. Reserve 1 cup of pasta water, then drain the pasta.
Slice a handful of the cherry tomatoes in half and leave the remaining tomatoes whole.
Heat the olive oil in a large skillet over low heat. Add the chopped garlic and crushed red pepper flakes. Cook for about 1 minute until fragrant, making sure the garlic does not brown.
Add the cherry tomatoes to the skillet and cook over medium heat. Once the tomatoes begin to soften, season with salt.
Gently press the whole cherry tomatoes with the back of a spatula to burst them and release their juices. Continue cooking for 8–10 minutes until the tomatoes create a thick, chunky sauce.
Stir in 1/2 cup of the reserved pasta water and allow the sauce to simmer gently for 1 minute.
Add a pinch of sugar if desired and adjust salt to taste.
Lower the heat and add the cooked spaghetti to the skillet. Toss thoroughly until the pasta is evenly coated in the sauce.
Remove the skillet from the heat. Add torn fresh basil and grated Parmesan cheese. Toss again until combined.
Serve immediately with extra Parmesan and a drizzle of olive oil if desired.