Use a box grater to grate the heirloom tomatoes into a medium mixing bowl.
Stir in the olive oil and garlic then season with salt. Let sit to marinate for 10 minutes.
Bring a large pot of salted water to a boil over medium-high heat. Add the ditalini pasta and cook until the noodles are al dente, about 8 minutes. Reserve ½ cup (120g) 1of the pasta cooking water then drain the pasta.
Add the marinated, grated tomatoes and stir to combine over low heat. Add the Parmesan and ¼ cup (60g) of the pasta cooking water, stirring to combine until the cheese evenly melts into the sauce.
Divide among serving bowls and top with the basil.
Notes
Add a thin layer of olive oil over the top then refrigerate in a sealed container for up to 3–4 days. Freeze in airtight containers for up to 2 months and thaw before using.