Make Filling
Sauté onion and celery with butter and salt until softened.
Add flour and toast for 1 minute.
Add Vermouth, scraping bottom.
Whisk in chicken broth, heavy cream, and thyme.
Simmer.
Add frozen vegetables and simmer.
Stir in chicken and simmer.
Season to taste.
Make Biscuits
Combine dry ingredients.
Pour in cold heavy cream and stir to make dough.
Knead 30 seconds on floured surface.
Pat into ¾" thick circle.
Cut into 8 pieces.
Bake at 450°F for 15 minutes.
Serve
Spoon filling onto biscuits.