Heat olive oil in a pan over medium-high heat. Season the chicken with salt & pepper and sear for 2 minutes per side until lightly golden (don’t cook through). Transfer the chicken to the slow cooker.
In the same pan, add onion and cook for 2 minutes, stirring. Add garlic and cook for another 30 seconds until fragrant. Pour in the white wine and let it simmer for 2-3 minutes, stirring, until reduced by half. Deglaze by scraping up any browned bits for extra flavour. Transfer the onion-wine mixture to the slow cooker.
Add chicken stock, tarragon, and Dijon mustard, salt, some more pepper and the cornflour. Cover and cook on LOW for 4 hours or HIGH for 2 hours, until the chicken is tender.
Stir in the crème fraiche and mix well.
Serve & Enjoy!
