Heat the fat in a medium-size saucepan. Add the onion, sage, and thyme, and sauté over medium-low heat, about 3 minutes. Stir in the flour, and whisk over low heat until a paste has formed and the flour is lightly colored, 2 to 3 minutes.
Add the milk and bouillon cubes, and whisk until smooth. Bring to a boil, then reduce the heat and cook over low heat, stirr