Melt butter in a large pan over medium heat.
Cook onion on medium-low for about 20-25 minutes, stirring occasionally, until caramelized.
Add tortellini to the onion, and add the bone broth.
Bring to a simmer and cook on low, covered, until pasta is al dente.
Remove from heat, add Parmesan and stir until creamy.
Serve!
