Place the butter in a med-large saucepan and melt over medium heat. Add the onion and garlic and sauté for 15 minutes, until the onion becomes nice and brown. Stir in the flour and continue to cook for one minute.
Stir in the flour and continue to cook for one minute.
Add the chicken stock, brandy, sage leaves, bay leaves, and 1 teaspoon of pepper and continue to stir (don't add salt yet because you want to see how salty your drippings are). Bring the mixture to a boil then lower the heat and simmer for 20 minutes, stirring occasionally.
Remove the gravy base from the heat and allow it to cool for one hour. Strain the cooled mixture through a fine-mesh sieve and set it aside or in the refrigerator if making it ahead of time.
If you are making the base ahead of time, cover the surface with plastic wrap to prevent a film from forming and refridgerate until you are ready to use