Add olive oil into a medium pan and place over high heat. When hot, place shrimp in a single layer, cook for one minute (without disturbing), turn them over and cook for an additional 30 seconds or cooked. Transfer shrimp to a plate and return pan back to heat, Reduce heat to medium.
Add butter. Once melts, add onion, garlic and red pepper flakes. Cook for 1-2 minutes until translucent. Stir in flour and saute for about 30 seconds, until raw smell of flour is gone.
Add remaining ingredients (one can stock, 1/2 cup heavy cream, 1/4 cup milk, 1 teaspoon Italian seasoning, 1/4 cup parmesan, 2 handfuls spinach, salt and pepper). Increase heat to high, let it come to a boil and cook for about 2 minutes until spinach is wilted. Take off heat, stir in shrimp along with any accumulated juices.
Serve best shrimp soup hot with a crusty bread, if desired.