Peel and cube the Russet potatoes. Place in a large pot, cover with salted water, and boil for 15-20 minutes until fork-tender. Drain and mash with heavy cream and unsalted butter. Season with salt and pepper, keeping warm.

Heat a large skillet over medium-high heat and add olive oil. Sauté the large shrimp seasoned with salt and pepper for 2-3 minutes per side until pink and opaque. Remove and keep warm.

In the same skillet, lower heat to medium, add minced garlic, and sauté for about 1 minute until fragrant. Add chicken broth, scraping the browned bits. Stir in heavy cream and Parmesan cheese until smooth and bubbly, then add lemon juice.

Return the shrimp to the skillet, coating in the sauce while heating through for 1-2 minutes. Serve on plates with mashed potatoes topped with shrimp and sauce. Garnish with parsley and optional Parmesan.