Season the chicken breasts with salt and pepper.
Heat the olive oil in a large heavy skillet over medium-high heat. Once hot, add the seasoned chicken breasts to the skillet. Sear for 4-5 minutes on each side until golden brown. Reduce the heat to medium, cover the skillet, and cook for an additional 5-7 minutes. Remove from the skillet and set aside.
Add the red onion to the same skillet and sauté for 3-4 minutes over medium heat until soft and translucent. Stir in the paprika, chicken stock, and heavy cream. Simmer for 5 minutes, stirring occasionally.
Whisk the cornstarch with a tablespoon of water in a small bowl to make a slurry. Gradually whisk the slurry into the sauce and cook for 3-5 minutes, stirring constantly, until the sauce thickens.
Add the tarragon and stir for another 1-2 minutes. Return the chicken breasts to the skillet. Spoon the sauce over the chicken breasts and simmer for 2-3 minutes over low heat.
