Season chicken cutlets with Essence, lightly dredge in flour, shake off excess, and set aside. Heat 1 tablespoon vegetable oil in a large skillet set over medium-high heat. Add chicken to pan, in batches if necessary, and cook 3 to 4 minutes per side until nicely browned and just cooked through. Set browned chicken aside.
Reduce heat to medium-low and add remaining 2 tablespoons vegetable oil to pan juices. Add 2 tablespoons flour, whisking continuously, and cook until mixture becomes blond in color. Whisk in cream and chicken stock and cook until slightly thickened, about 3 minutes. Add onion and continue cooking until soft, about 3 minutes. Stir in mustard and tarragon. Return chicken cutlets to pan and heat through, basting continuously. Remove from heat and garnish with chives. Serve immediately.