Preheat oven to 500 degrees.
Season chicken with salt and pepper.
Heat an oven proof skilled over medium high heat. Once the pan is hot, add the grapeseed oil. Add the chicken breasts skins side down.
Cook the chicken without turning it for about 10 - 15 minutes or until the skin is a nice golden brown.
Flip the chicken over, add the pearl onions, and place in the oven for an additional 10-15 minutes or until the internal temperature reaches 165°F.
Remove from oven, remove the chicken and the onions from the pan. Tent with foil to keep warm and rest.
Return the pan to the stove over a medium heat. Add port wine and deglaze the pan making sure to scrap up all of those wonderful brown bits!
Add chicken stock, Dijon mustard, lemon juice, thyme, and tarragon. Reduce heat to simmer and reduce down for about 5 minutes.
Make a slurry with the cornstarch and reserved chicken broth. Cook for an additional 2-3 minutes until slightly thickened.
Stir in parsley and serve under not over the chicken so that the skin maintains its crispiness.