Add 1 tablespoon vegetable oil to a large oven-proof skillet set over medium-high. Once the oil is hot, add the chicken and brown it on all sides. (It does not need to be cooked completely.) Using a slotted spoon, remove the chicken to a bowl and set it aside.
Reduce the heat to medium-low. Add the remaining 1 tablespoon vegetable oil to the skillet then add the onions and garlic and cook, stirring as needed, until the onions are caramelized, about 35 minutes.
Increase the heat to high then add the sherry, and cook while scraping up any brown bits, for 1 minute. Stir in the flour then cook for 2 minutes.
Stir in the beef bouillon paste, Worcestershire sauce, heavy cream and 1 1/4 cups water. Simmer the sauce for 2 minutes.
Stir in the browned chicken and thyme. Bring the mixture to a simmer and cook until the sauce has thickened slightly, about 5 minutes, then remove the skillet from the heat.
Set the oven to BROIL.
Arrange the baguette toasts in a single layer on top of the chicken mixture so that they are overlapping slightly. Sprinkle the cheese on top then place the skillet several inches under the broiler and broil until the cheese is melted and the toasts are slightly crisped, 3 to 5 minutes.
Remove the skillet from the oven, garnish with additional fresh thyme and serve.