Cook the pasta as per package instructions and set aside.

In the meantime, heat 1tbsp olive oil in a saute pan; add onions and leeks and cook on medium flame, stirring occasionally until lightly browned around the edges. Add the minced garlic and continue to cook on medium-low flame until golden brown and caramelized, this will take anywhere between 20-30 minutes.

Add the stock and deglaze the pan; add tomato paste and thyme. Bring the mixture to a simmer.

Slowly stir in heavy cream and balsamic vinegar. Simmer until the mixture thickens just a little bit. Season with salt and pepper and red pepper flakes (if using).

Turn off the heat and add Arugula/ spinach. Stir in the cooked pasta and mix well to combine. Serve immediately topped with Parmesan cheese (if using).