Heat your non-stick skillet over medium heat and add a generous pat of butter, listening for a gentle sizzle as it melts and shimmers.
Place the slices of bologna in the skillet, making sure they lay flat and aren’t overlapping.
Cook the bologna undisturbed for about 2-3 minutes, watching as the edges turn a deep golden brown and crispy, and the meat begins to sizzle.
Carefully flip each slice using a spatula and cook the other side for another 2 minutes, until both sides are golden and crispy, and the bologna is caramelized around the edges.
If using cheese, place the slice of cheddar on top of the bologna now and cover the skillet briefly to allow it to melt into a gooey layer.
Meanwhile, toast your bread slices until golden brown and buttered, either in a toaster or in the same skillet for extra flavor.
Spread mustard or your preferred condiment on one side of each toasted bread slice, then layer the crispy bologna with melted cheese onto one slice.
Top with the second slice of bread, press gently to ensure everything sticks together, and let it sit for a minute to settle the flavors and juices.
Cut the sandwich in half if desired, revealing the crispy edges, melty cheese, and smoky slices, then serve immediately and enjoy the satisfying crunch and savory aroma.