Combine leftover sauce and broth and heat through in a saucepan over medium heat.
No Leftover Sauce
Melt butter in bottom of large sauce pan. Add onions and cook over medium heat about 5 minutes. Add mushroom bits and cook another 5 minutes or so. Add garlic and cook 1 minute more. Sprinkle the flour over the vegetables and stir until the flour is moistened and coats the vegetables.
Add broth and simmer about 5 minutes.
Add brandy and cider and pepper and simmer 10 minutes.
Reduce heat to medium low. Add salt and ¼ cup of cream and heat through. Do not boil.
Put corn starch in a small dish and dissolve with remaining ¼ cup of cream. Add cornstarch mixture and salt to the mixture and stir until mixtures thickens.
You can serve in soup bowls as is or add a puff pastry topping as per below.
Topping (Optional)
Preheat oven to 400 degrees.
Roll out puff pastry. Use the soup bowl to cut out puff pastry pieces the size and shape of the mouth of the bowl.
Spray 4 oven proof soup bowls with cooking spray. Fill the soup bowl with soup. Leave ½"-1" clearance at top of the bowl.
Top the bowl with puff pastry. Press the dough onto the rim of the bowl to secure it. Cut a slit in the center to allow steam to vent.
Bake about 35 minutes until pastry is done and golden brown.
Notes
If you want freeze this soup, cool completely and seal in a freezer proof container. You can thaw and proceed to reheat on stove top or divide among bowls, add the puff pastry and reheat in the oven about 35 minutes at 400 degrees.