Peel and quarter the russet potatoes, placing them in a large pot filled with cold salted water. Bring to a boil over high heat and cook until fork-tender, about 15-20 minutes. Drain the potatoes well, return them to the pot, and mash with butter and heavy cream until smooth and creamy. Season to taste with salt and pepper.

In a large skillet, heat 2 tablespoons of olive oil or butter over medium heat. Once hot, add minced garlic and sauté for about 1 minute until fragrant but not browned. Next, carefully add the large shrimp, cooking for 2-3 minutes per side until they turn pink and opaque. Once cooked, remove the shrimp from the skillet and set aside, keeping them warm.

Using the same skillet, pour in 1 cup of chicken broth and bring to a gentle simmer over medium heat. Stir in ½ cup of heavy cream, freshly grated Parmesan cheese, and a squeeze of lemon juice. Allow the mixture to simmer for 3-5 minutes until slightly thickened, stirring occasionally. Taste and adjust the seasoning with salt, pepper, and optional red pepper flakes for a hint of heat.

Return the cooked shrimp to the skillet, tossing gently in the creamy garlic sauce to combine. Let everything cook together for an additional 1-2 minutes, ensuring the shrimp are heated through and coated in the sauce. To serve, scoop a generous portion of the mashed potatoes onto plates and top with the creamy garlic shrimp, garnishing with freshly chopped parsley for a touch of color.