If you can buy thin cut chicken use that if, if not, slice your chicken breast lengthwise to create thinner breasts.
In a bowl combine sour cream, granulated onion and garlic. Add chicken and coat evenly. Place in the fridge for 30 min- 1 hour.
Preheat oven to 400 degrees
In an oven safe skillet melt 2 tablespoons of butter. Add onions and cook on medium heat for about 20 minutes or until soft.
Remove onions from skillet. Add remaning butter and oil. Turn heat up to Medium high. Add chicken breasts-with the sour cream coating still on. Sprinkle with salt and pepper.
Saute chicken on each side for 3-4 minutes or until brown. They will not be cooked through.
Remove chicken to same plate as onions.
Sprinkle flour into pan. You might need to add a bit more butter to create a paste. Let cook 1-2 minute. Add beef broth. Whisk until smooth.
Add chicken back to skillet and top with onions. Arrange baguette slices on top of onions. Top with cheeses. Place into oven for 15-20 minutes or until cheese if bubble and golden. Sprinkle with chives. Serve.