Boil the pasta. Bring a large pot of well-salted water to a boil. Cook pasta until just shy of al dente so it finishes in the sauce.
Reserve at least 1 cup of pasta water before draining.
Sauté the aromatics. In a large skillet, warm 1–2 tablespoons olive oil or sundried tomato oil over medium heat. Add garlic and a pinch of red pepper flakes. Cook for 30–60 seconds until fragrant, not browned.
Add sundried tomatoes. Stir in the sliced sundried tomatoes and cook for 1–2 minutes to soften and infuse the oil.
Start the sauce base. Add a generous splash (about 1/2 cup) of hot pasta water to the skillet.
Reduce heat to medium-low and whisk in the mascarpone until smooth and creamy.
Season and brighten. Stir in lemon zest and a squeeze of lemon juice. Add half the parmesan. Taste and season with salt and black pepper.
The sauce should be slightly loose.
Toss with pasta. Add the drained pasta to the skillet. Toss vigorously, adding more pasta water as needed until the sauce coats the pasta and looks glossy.
Finish and serve. Stir in fresh basil and the remaining parmesan. If using spinach, wilt it in now; if adding cooked chicken or pancetta, fold it through.
Serve immediately with extra parmesan and a final crack of pepper.