Heat the olive oil in a high-walled dutch oven pot over medium heat. Add the garlic and cook until lightly fragrant and golden, then remove it from the oil.
Add the zucchini rounds to the oil and cook on each side for about 3-5 minutes or until starting to turn golden brown. Remove from the pot with a slotted spoon, shaking off any excess oil, and place on a paper towel-lined plate. Sprinkle with salt and pepper. Continue this process until you've cooked all the zucchini.
Start cooking your pasta during your second to last batch of zucchini and cook until al dente according to package directions. Reserve 1 cup of the pasta water and drain your noodles.
Pour the leftover zucchini-infused oil into a small bowl and set aside. Remove about 1 cup of the cooked zucchini (which will only be about a third of the total amount) to either a tall jar if using an immersion blender or the bowl of a food processor along with 1/4 cup of the pasta water and 1 tablespoon of the reserved oil. Blend until smooth, adding more pasta water as needed to thin the sauce.
With the high-walled pot back over medium-low heat, add the spaghetti, butter, and zucchini sauce. Use tongs to stir everything together until the noodles are well-coated and the butter has melted. Add more salt and fresh black pepper, to taste.
Serve with torn fresh basil leaves and a drizzle of the remaining zucchini-infused oil. Plus a sprinkle of Maldon salt (optional).