Cut 1 onion into cubes. Heat 2 tablespoons oil in a pan over medium-high heat. Add 300 g chicken breast strips and cook for 6-8 minutes, stirring occasionally, until the chicken is no longer pink inside.
Pour 200 ml white wine into the pan to deglaze, scraping up any browned bits. Add 2 teaspoons dried tarragon and season lightly with salt and pepper (the sun-dried tomatoes are salty, so use restraint).
Reduce heat to medium and simmer for 3-5 minutes. While simmering, cut 100 g sun-dried tomatoes into strips.
Add the sun-dried tomatoes and 4 tablespoons crème fraîche to the pan. Simmer for 5-7 minutes, stirring occasionally, until the sauce is creamy and the chicken is cooked through (internal temperature 74°C/165°F).