In a microwave-safe bowl or measuring cup, combine the stock and bouillon cubes. Heat for one minute, then stir well. Repeat this process, heating in increments and stirring, until the bouillon cubes are completely dissolved.

In a saucepan over medium-high heat, melt the butter. Sprinkle in the flour, onion powder, thyme, sage, and rosemary. Cook for about a minute, allowing the flour to cook off and the spices to release their aromas. Gradually pour in the warm stock, whisking continuously to create a smooth consistency. Bring the mixture to a boil, then reduce the heat to a simmer. Continue whisking until the gravy reaches a thick, silky texture, approximately one minute. Season with salt and pepper to taste, then remove from heat and serve while hot.