To make the Cream of Mushroom Soup:
- Heat oil in a skillet over medium heat.
- Add garlic, mushrooms and pancetta and saute over medium heat for 5 minutes.
- Remove from pan and set aside.
- Melt 2 Tbsp butter in the skillet.
- Add flour and whisk to combine.
- Slowly add broth and then milk and salt, whisking constantly to combine.
- Bring to a boil, then reduce heat to a simmer and whisk constantly for 2-3 minutes to thicken.
- Add mushroom mixture back in, stir to combine, then remove from pan and set aside.
For the casserole:
- Preheat oven to 350 degrees F.
- Bring a large pot of water to a boil. Add green beans and boil for 5 minutes.
- Drain and run under cold water to stop cooking. Set aside.
- Meanwhile, melt 2 Tbsp butter in a skillet.
- Add sliced mushrooms, garlic and salt and saute for 5 minutes.
- In a 9×9 pan, combine green beans, sauteed mushrooms and cream of mushroom soup.
- Top with panko breadcrumbs and bake 20 minutes F.
- Sprinkle with French fried onions just before serving.