Heat oil in a large pot or deep skillet over medium; cook garlic 1 minute until fragrant.
Add tomatoes and optional pepper flakes; stir another minute.
Add broth; boil, add penne, and stir to submerge.
Reduce heat to medium; cook 12-15 minutes, stirring occasionally, until pasta is almost al dente and most liquid absorbed.
Add cream, spinach, and Parmesan; cook 2-3 more minutes until spinach wilts and sauce thickens.
Season with salt and pepper to taste, garnish with fresh basil, and serve immediately.