In a medium pot, melt 4 tablespoons of butter on medium low and add flour stirring constantly to create a roux. Be careful not to burn flour and once all the flour and butter is incorporated and lightly browned, add cream and milk slowly, stirring constantly. Add salt, pepper, and sage.
Turn down heat down a little so milk doesn't burn and reduce for at least 30 minutes or until it's reached desired thickness.
Meanwhile, in a large saute pan with melt 2 tablespoons of butter on medium heat and add mushrooms. Saute until almost all the moisture is cooked off.
Add soup to mushrooms in saute pan and mix well. Add chicken stock and mix well until combined. Continue to cook and reduce for another 10-15 minutes until desired thickness is reached.
Remove from heat and let cool. Transfer to jars for canning or freezer bags to freeze.
Yields approximately 5 cups.