Begin by melting the butter in a large pot over medium heat.
Add the diced onion, minced garlic, kosher salt, and black pepper, then cook them gently for around 6 minutes, stirring now and then until the onion softens.
Pour in the balsamic vinegar and mix it into the sautéed vegetables.
Stir in crushed tomatoes, broth, heavy cream, and bay leaves, then bring everything to a rolling boil.
Lower the heat to maintain a gentle simmer and cook uncovered for 5 minutes to let the flavors meld.
Add the tortellini to the pot and simmer until the pasta is tender, usually between 5 to 6 minutes; if using fresh tortellini, start checking doneness at 3 minutes.
Once cooked, remove the pot from heat and take out the bay leaves.
Fold in the thinly sliced fresh basil to infuse more aroma.
Serve in bowls and sprinkle with Parmesan cheese and additional basil leaves if you like.
