Prepare Ebly according to the instructions on the package.
Peel and dice the onion and roast in a little melted butter. Now add the meat and roast it too. Drain and add the mushrooms. Season with salt and pepper, pour in the broth and let simmer for a few minutes. Add flour and stir well. Remove the pan from the heat, stir in the tarragon mustard and refine with sour cream and parsley.
Arrange the meat on plates and serve with the Ebly.