Season the chicken with salt and pepper.
Kosher salt and freshly ground black pepper, 8 boneless skinless chicken breasts
In a large skillet, melt the butter over medium heat. Add the onions and let cook until they are tender. Push them to the outside edges of the pan.
2 tablespoons unsalted butter, 1 small onion, diced fine
Turn the temperature up to medium-high and sear both sides of the chicken for 1-2 minutes until golden brown.
8 boneless skinless chicken breasts
Remove the chicken from the pan for the moment.
Reduce the heat to medium and add the whole peeled garlic cloves. Cook until golden brown and tender, stirring often.
40 cloves garlic
Return the chicken to the pan and add the chicken stock. Sprinkle the tarragon into the pan, then bring to a boil.
1-½ cups chicken broth, 1 tablespoon dried tarragon
Reduce the heat to a simmer, cover the pan and let the chicken cook for 25-30 minutes until it is cooked through.
To create the sauce, mix the milk and flour together in a small bow. Pour into the hot pan and stir to combine. Cook for a couple minutes until the sauce thickens.
2 tablespoons all-purpose flour, 2 tablespoons milk
Serve hot with pasta, rice or potatoes, if desired.