Start by preheating the cast iron skillet or grill pan over medium heat. Slice the apple but just before assembly to prevent browning and combine both grated cheeses.
Add a tablespoon of olive oil to the skillet and warm the oil. Once warm add the sliced shallots, thyme and sauté for 8-10 minutes on medium heat until caramelized stirring frequently. Once done transfer the shallots to a plate and set aside.
Chop the Swiss chard and sauté the greens with chopped garlic, until wilted and garlic is slightly brown in the same pan, you may need to add a little oil. Once done transfer the greens.
Spread mustard on both slices of the bread to cover the entire surface of the bread. Spread a little cheese over the mustard and lay 3-4 slices of thinly sliced apple on top.
Spoon the caramelized shallots and the sautéed greens on top. Add the cheese on top of the greens in an even layer and place the second slice of bread. Brush a little olive oil on the slice of bread and place it in the skillet, oiled side down.
Cover with a weighted press and cook for two minutes until toasty and cheese starts to melt. Flip the sandwich over, brush with a little olive oil if needed and cook for another two minutes until the cheese is melted through.
Cut in half and serve warm. Serve as is or accompany any soup or salad Tasty!!