Add the butter to a large skillet over medium high heat.
Once the butter is melted, add the onions and let cook for 2 minutes.
Add the garlic and cook for another minute.
Add the sliced mushrooms, salt, and pepper and cook, stirring occasionally for 10 minutes.
Sprinkle the chickpea flour over the mushrooms, and stir together.
Add the broth and miso paste and stir until all the miso has dissolved.
Add the remaining ingredients and stir together.
Bring to a boil and stir consistently until mixture has thickened, about 5-7 minutes.
Taste and adjust the seasoning with salt and pepper if needed.
Serve immediately or let cool completely and store in an air tight container.