Combine 1/2 cup flour & salt in a bag. Add chicken & shake to coat.  Add butter & oil to a saute pan, medium high. Brown chicken on both sides, 8-10 minutes. Set on paper towls to drain excess oil, then add to slow cooker. 
Saute onion for 10 minutes, medium high.  Add 2 tbsp flour & cook, stirring constantly. Gradually add wine, scraping the bits off the bottom. Add the stock & cook for 10-15 minutes, until sauce thickens.  Pour sauce over chicken & add 2 sprigs of the fresh tarragon.

Cook on low 6-8 hours.

About 10-15 minutes before serving, add cream. Remove tarragon stems. Chop the remaining 4 tarragon sprigs & sprinkle over chicken.

I'll be honest - I've never tried this recipe. I found it online & have intended on making it for some time now, but have never actually cooked it. Please comment if you try it! Let me know how it is, and if you have any changes/suggestions/substitutions that would improve it!