Pour the olive oil into a medium saucepan and add the smashed garlic. Set the heat to medium-low and cook gently, stirring occasionally, until the garlic becomes fragrant, about 2 minutes. Stir in the rosemary and a pinch of red pepper flakes, letting the mixture cook for another minute until the herbs are aromatic.

Remove the pan from the heat and mix in the tomato paste until combined. Pour in 2½ cups of water and return the saucepan to the stove. Turn the heat up to high, bringing the mixture to a rolling boil. Stir in the pasta and season generously with kosher salt. Continue cooking, stirring regularly, until the pasta is tender but firm to the bite (al dente), which should take about 12 minutes.

Once the pasta is cooked, take the saucepan off the heat and fold in the Parmesan cheese. Taste the dish and adjust the seasoning with more salt and freshly ground black pepper if needed.

Divide the pasta between two bowls or plates, and garnish with fresh basil leaves. Serve immediately. Store any leftovers in an airtight container and refrigerate for up to 3 days.