Prepare the Mashed Potatoes: Place peeled and cubed potatoes in a large pot filled with salted water. Bring to a boil and cook for about 15 minutes until fork-tender. Drain and return to the pot. Add butter and warm milk, mash until creamy and fluffy, season with salt, and keep warm.

Cook the Shrimp: Toss large shrimp with olive oil, paprika, garlic powder, salt, and pepper. Heat a skillet over medium-high heat, add shrimp in a single layer, and sear for about 2-3 minutes on each side until pink and opaque. Remove and set aside.

Make the Creamy Garlic Sauce: In the same skillet, melt butter, sauté minced garlic for 1 minute. Pour in heavy cream and stir in Parmesan cheese and Dijon mustard if using. Simmer for 3-5 minutes until thickened, and season with salt and pepper.

Assemble the Dish: Scoop mashed potatoes onto each plate, top with sautéed shrimp, drizzle with garlic cream sauce, and garnish with fresh thyme leaves. Serve immediately.