Preheat your oven to 400°F (205°C). Peel the garlic cloves but keep them whole. Wrap them in aluminum foil with a drizzle of olive oil and roast for about 20 minutes until soft and golden.
While the garlic roasts, bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente—usually about 8-10 minutes. Drain and set aside, reserving a little pasta water for later.
Pat the steak dry with paper towels, then season generously with salt and pepper on both sides. Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Once hot, add the steak and sear for about 4-5 minutes per side. Remove from skillet and let rest for a few minutes before slicing thinly against the grain.
In the same skillet, reduce the heat to medium. Add the remaining tablespoon of olive oil, then squeeze the roasted garlic cloves out of their skins and mash them lightly with a fork. Pour in the heavy cream and stir to combine. Bring the mixture to a gentle simmer, then whisk in the grated Parmesan cheese until the sauce is smooth and creamy. Season with salt and pepper to taste.
Add the cooked spaghetti to the skillet with the Alfredo sauce, tossing gently to coat. If the sauce feels too thick, add a splash of the reserved pasta water to loosen it up. Finally, fold in the sliced steak to warm it through and distribute it evenly.
Divide the pasta between plates or bowls. Sprinkle fresh chopped parsley over the top for a pop of color and freshness. Serve immediately, and enjoy the comforting blend of flavors and textures.