1. Begin by preparing the mashed potatoes. In a large pot, boil the cubed potatoes in salted water until tender, about 15-20 minutes. Drain and return them to the pot.
2. Add 2 tablespoons of butter, milk, and sour cream to the potatoes. Mash until smooth and creamy, adjusting the seasoning with salt and pepper to taste. Cover to keep warm.
3. In a large skillet, melt the remaining tablespoon of butter over medium heat. Add the minced garlic and sauté until fragrant, about 1 minute.
4. Add the shrimp to the skillet. Cook until pink and opaque, about 2-3 minutes per side. Remove the shrimp from the skillet and set aside.
5. In the same skillet, add the heavy cream and Parmesan cheese. Stir continuously until the cheese has melted and the sauce has thickened, about 3-4 minutes.
6. Return the shrimp to the skillet, tossing them in the creamy garlic sauce to coat well. Taste and adjust seasoning if necessary.
7. To serve, spoon the creamy garlic shrimp over a bed of mashed potatoes. Garnish with chopped fresh parsley for a pop of color and freshness.

This dish is a testament to the simple pleasures of cooking at home. The creamy garlic sauce is rich and aromatic, perfectly complementing the tender shrimp and fluffy potatoes.