Adapted from the classic French dish Poulet au Vinaigre, which depends on flour and heavy cream, and takes over an hour to cook. As the chicken cooks, the acid in the vinegar tenderizes and the vinegar flavor mellows. The vinegar softens and lightens the heaviness of the fats from the milk and chicken.
Wash, dry and sprinkle the chicken with salt. Ideally do this a day ahead of time, in which case, cover and place in the refrigerator.
When ready to cook, set the Instant Pot to Saute. Dredge the chicken in flour and place on a wire rack to rest. Once the pot is hot, add olive oil to coat the pan. Sear the chicken (skin side down if applicable), browning in batches so as not to overcrowd the pot. Cook 4 minutes per side, then remove the chicken to a plate. Pour off the excess fat.
Add the ghee, onions and a pinch of salt to the pot. Saute the onions, being sure to scape the bottom of the pot clean. Sprinkle with some water if it helps. Cook onions until they are soften and start to brown, but avoid burning. Add the wine, vinegar, most of the tarragon, and the coconut milk. Stir and bring to a boil. Add the chicken, pressure down into the sauce.
Cover the Instant Pot with the lid, lock and close the vent. Click cancel to end "Saute" function, then set to Pressure Cook on High for 10 minutes. Allow Natural Pressure Release (about 10-15 minutes).
Remove the chicken to a platter and saute to thicken the sauce. Taste and add a splash of vinegar if needed to brighten. Serve chicken with spoon-full of sauce and garnish with a sprinkle of tarragon.