Heat the milk in a saucepan. In a small pot, melt the butter and sauté the garlic and shallots together. Add the flour and cook, stirring, until it turns a light golden color, being careful not to burn it. Gradually add the hot milk, stirring well to avoid lumps.

Add 1/2 chicken bouillon cube and a pinch of salt. Cook for about 15 minutes, stirring occasionally so it doesn't stick to the bottom. Add the mustards and parsley, and stir. If the sauce is too thick, add more milk. Taste and adjust salt as needed.