Begin by preparing the mashed potatoes. Place the cubed potatoes in a large pot and cover with cold water. Add a pinch of salt and bring to a boil over medium-high heat. Cook until the potatoes are fork-tender, approximately 15-20 minutes.
While the potatoes are cooking, melt 2 tablespoons of butter in a large skillet over medium heat. Add the minced garlic and sauté for about 1 minute, until fragrant but not browned.
Add the shrimp to the skillet, seasoning with salt and pepper. Cook for 2-3 minutes on each side until the shrimp are pink and opaque. Remove the shrimp from the skillet and set aside.
In the same skillet, pour in the chicken broth, scraping up any bits from the bottom. Allow it to simmer for about 2 minutes before adding the heavy cream.
Stir in the grated Parmesan cheese and Italian seasoning, mixing well. Allow the sauce to simmer for 3-4 minutes until it thickens slightly.
Return the cooked shrimp to the skillet and toss to coat in the creamy sauce. Heat through for another minute, then remove from heat.
Once the potatoes are tender, drain them and return them to the pot. Add the remaining butter, milk, and sour cream. Mash until smooth and creamy. Adjust seasoning with salt and pepper to taste.
To serve, spoon the creamy garlic shrimp over a generous portion of mashed potatoes. Garnish with fresh parsley for added flavor and color.