Take two boneless skinless chicken breasts and butterfly them, slicing all the way through. This will create four thin cut chicken breasts.
On a plate, combine ¼ cup flour (saving the rest for later), salt, pepper, and italian seasoning.
Dredge each chicken piece in the seasoned flour mixture.
Heat an oven safe large skillet over medium heat to melt 2 tbsp. butter.
Add in chicken pieces. Cook until they are golden brown, about 5 minutes on each side. Remove to a plate to the side.
To the same skillet, add remaining butter. Reduce heat to medium low and add in sliced onions and cook down until they are brown and soft, 15-20 minutes. Stirring every 4-5 minutes.
Add remaining flour and stir to create a roux. Cook for 1-2 minutes.
Stir in white wine, beef stock, soy sauce, and thyme sprig. Allow to simmer for 5 minutes to cook down and thicken.
Turn your oven broiler on High.
Add chicken back in, nestling it among the onions. Top chicken and onions with cheese, and place in preheated oven.
Broil for 5 minutes, or until the cheese is brown and bubbly. Watch carefully to avoid burning.