Creamy Dijon Chicken - Koops Mustard

Ingredients

• 1 medium onion, thinly sliced
• 1/4 cup butter
• 4 to 6 boneless chicken breast halves
• 1 cup heavy cream
• 2 tablespoons Koops’ Dijon mustard
• 1 teaspoon dried leaf tarragon
• 1/2 teaspoon salt
• 1/4 teaspoon freshly ground pepper
• 1/2 cup sour cream