- In a large sauté pan, over medium-high heat, melt the butter. Add the sliced onion, salt and thyme sprigs. Cook the onions, stirring frequently until a dark golden brown, being careful not to burn them. This should take about 20 minutes. Remove from the heat. Discard the thyme stem. Set aside.
- Preheat your oven to 375 degrees.
- Place the sliced baguette pieces on a wire rack. Toast the bread in the oven on the rack for about 10 minutes, checking often. Remove when done.
- Turn your oven on to the broil setting.
- Place a slice of Gruyère on each slice of bread. Return the baking rack to the oven. Broil until the cheese begins to bubble and melts.
- Top each slice with a bit of the caramelized onion and a slice of apple. Drizzle with a bit of honey and a sprinkling of cayenne pepper, if desired.