- In a large skillet, melt butter over medium-low heat.  Stir in chopped onions and allow to soften. 
- Add in garlic cloves and cook for 30 seconds until fragrant. 
- Stir in remaining ingredients except for the heavy cream and bring to a simmer. 
- Cook for 30 minutes.  Use an immersion blender to blend until smooth. 
- Stir in heavy cream and serve with grilled cheese.