Melt butter in a large deep skillet over medium heat.
Add onions and cook, stirring occasionally, until translucent and starting to brown slightly, about 3-5 minutes.
Stir in the flour and season with salt and pepper.
Pour in the chicken stock and stir until blended with the flour.
Slowly pour in the half-and-half while stirring until well-blended. Raise the heat and cook until thickened, stirring constantly, about 1-2 minutes.
Stir in the tarragon, peas and chicken and cook a few more minutes or until warmed through. Season with salt and pepper as needed.
Serve over biscuits, or as desired.
