3 tablespoons unsalted butter, divided
1 whole chicken, cut into 10 pieces and patted dry
1/2 cup all-purpose flour
1 onion, cut into thin slices
1/2 cup white wine or champagne
2 cups chicken stock
4-5 sprigs fresh tarragon
2 egg yolks
1/2 cup heavy cream
1 tablespoon fresh tarragon, minced
Juice of 1/2 lemon
Kosher salt and freshly ground pepper, to taste