Melt butter in a large skillet, over medium-high heat. Add onion and sauté for 2-3 minutes, until translucent. Add garlic and sauté for 1-2 minutes, until fragrant.

Pour the marinara sauce into the skillet and stir to combine. Reduce heat to medium-low, add the salt, pepper, cream, and harissa sauce. Simmer for about 5 minutes, stirring occasionally.

While the sauce is simmering, bring a medium-sized pot of water to a boil, over high heat. Add fettuccine and bring to a second boil. If desired add a pinch of salt and drizzle of oil to avoid the pasta sticking together.

Reduce heat to medium, simmer un-covered for 5 minutes or so, until al-dente or preferred tenderness is achieved.

Strain cooked fettuccine and add to the sauce with basil and Parmesan. Toss to combine and simmer for 1-2 minutes.

Serve with basil and Parmesan as a garnish over the top.