1. Boil potatoes in a large pot of salted water until tender, about 15-20 minutes. Drain and return to the pot.
2. Add 2 tablespoons of butter, milk, sour cream, salt, and pepper to the potatoes. Mash until smooth and creamy. Cover and keep warm.
3. In a large skillet over medium heat, melt the remaining butter. Add shrimp and cook until pink, about 2-3 minutes per side. Remove and set aside.
4. In the same skillet, add garlic and sauté until fragrant, about 30 seconds. Stir in chicken broth and heavy cream, bringing to a simmer.
5. Add Parmesan cheese, stirring until the sauce thickens, about 5 minutes. Return shrimp to the skillet and coat with the sauce.
6. Stir in parsley and season with salt and pepper to taste. Simmer for another minute to let the flavors meld.
7. Serve shrimp and sauce over mashed potatoes, garnished with additional parsley if desired.

Personal tip: Keep an eye on the sauce to prevent it from becoming too thick—consistency is key to a perfect dish.