In a large saucepan or dutch oven pan, cook the bacon over medium heat until crispy. Remove the bacon with a slotted spoon and set aside. Add the diced shallots to the bacon grease and cook for about 3 minutes, until tender. Add the mushrooms, rosemary and garlic to the pan. Cook for about 5 minutes, until the mushrooms are tender and golden. Return the cooked bacon to the pan.
Sprinkle the flour over the mushrooms and bacon and stir to coat. Cook for about 1 minute, stirring constantly.
Pour the chicken broth into the pan. If desired, add a splash of marsala wine. Stir to combine. Bring the mixture to a simmer, stirring frequently. It should begin to thicken as it simmers. Simmer for a few minutes, then reduce heat and add the half and half.
Remove about a cup of the soup with a bunch of the mushrooms When cool enough to safely handle, blend the cup of soup until smooth. Return the blended mixture to the pan with the rest of the soup.
OR just use a stick blender right in the pan to make a lovely smooth soup.