Step 1: Preheat your oven to 400°F (200°C). Prepare the garlic for roasting: Slice off the top ¼ inch of each garlic bulb to expose the cloves. Drizzle with 1 tbsp olive oil, wrap tightly in foil, and roast for 35-40 minutes, or until cloves are very soft and caramelized.
Step 2: While the garlic roasts, bring a large pot of heavily salted water to a rolling boil. Add the giant pasta shells and cook according to package directions until al dente. Drain immediately and rinse with cold water to prevent sticking; set aside.
Step 3: Once garlic is roasted, remove from oven and let cool slightly. Squeeze the soft garlic cloves out of their skins into a small bowl and mash with a fork until smooth.
Step 4: In a medium saucepan over medium heat, melt the unsalted butter. Add the mashed roasted garlic and sauté for 1 minute until fragrant. Pour in the double cream (heavy cream), bring to a gentle simmer, then stir in the ½ cup (50g) finely grated Parmesan. Cook, stirring occasionally, until the sauce slightly thickens, about 3-5 minutes.
Step 5: Season the roasted garlic cream with salt and pepper to taste. If desired, add a pinch of nutmeg or white pepper for an extra layer of flavor. Remove from heat.
Step 6: Reduce oven temperature to 375°F (190°C). Take each cooked pasta shell and carefully stuff it with a generous amount of the roasted garlic cream. Arrange the stuffed shells in a single layer in a 9x13 inch baking dish.
Step 7: Sprinkle the remaining ½ cup (50g) grated Parmesan over the stuffed shells. Bake for 20-25 minutes, or until the cheese is melted and bubbly, and the edges of the pasta are slightly golden. Serve hot and enjoy!