01 - Spread butter evenly on one side of each slice of bread.
02 - If using Dijon mustard, spread it on the unbuttered side of two of the bread slices.
03 - On the unbuttered side of two bread slices, layer the cheddar cheese, Swiss cheese, and pickle slices. Top with the remaining bread slices, ensuring the buttered sides face outwards.
04 - Firmly press the exterior of each assembled sandwich into the crushed popcorn, ensuring both sides are coated evenly.
05 - Place a nonstick skillet or griddle over medium heat.
06 - Cook the sandwiches for 3 to 4 minutes on each side. Gently press them with a spatula while cooking until the bread achieves a golden-brown hue, the popcorn forms a crispy crust, and the cheese is thoroughly melted.
07 - Remove the sandwiches from the pan. Allow them to cool for 1 minute, then slice and serve immediately.