In the same pan, add butter and sauté garlic until fragrant (medium-high heat).
Add sundried tomatoes and chopped cherry tomatoes, cooking for about 5 minutes until tomatoes soften.
Add seasonings and stir for 30 seconds.
Pour in milk and cream, stirring until the mixture boils and becomes cohesive.
Stir in parmesan cheese and reserved pasta water, cooking until the sauce thickens. It should still be runny as it will thicken more when you add the pasta later.
Turn off the heat, then stir in chopped spinach and basil leaves. Adjust seasoning as needed.