Use a microwave-safe bowl or measuring cup. Add the stock and the bouillon cubes, then heat for 1 minute and stir. Repeat heating until the bouillon is dissolved.
In a saucepan over medium-high heat melt the butter. Add the flour, thyme, and sage and cook for 1 minute. Slowly whisk in the hot stock/bouillon cube until smooth. Bring to a boil then reduce to a simmer. Cook, whisking, until smooth and thick, about 1 minute.
Remove from heat, then salt and pepper to taste. Serve immediately.