Heat the olive oil in a large skillet over medium heat. Add the onions, salt, and pepper. Cook for 20–25 minutes, stirring occasionally, until deeply golden and jammy. Lower the heat if they start to burn!

Stir in the garlic and thyme and cook for 1–2 minutes. Add the balsamic vinegar and cook for another minute to deglaze the pan.

Pour in the vegetable broth and bring to a simmer. Add the uncooked pasta, making sure it’s mostly submerged. Simmer for 10–12 minutes, stirring occasionally, until the pasta is tender and most of the liquid is absorbed.

Reduce the heat to low and stir in the gruyère and parmesan until melted and silky. Add in the cream and stir until combined. Taste and adjust salt/pepper as needed. Top with extra cheese, fresh thyme, and lots of cracked black pepper.

Cheese – While it’s traditional in French onion flavors, I know gruyere can be quite expensive. Swiss cheese is the best affordable substitute, but mozzarella, white cheddar, or provolone also work well depending on what you have on hand.

Storage Instructions – Store leftovers in an airtight container in the fridge for up to 4 days. Reheat gently on the stovetop or in the microwave with a splash of broth or water to loosen the sauce.