Place a heavy skillet over medium heat and add a tablespoon of butter or oil, allowing it to warm until shimmering and fragrant.
Carefully lay the slices of thick-cut bologna into the hot skillet, making sure they’re not overcrowded.
Cook the bologna for about 3-4 minutes per side, watching as the edges turn a deep golden brown and crispy, and the fat begins to render out.
Flip the slices carefully with a spatula, and cook the other side until equally crispy and slightly curled at the edges.
While the bologna cooks, toast the bread slices in a toaster or in a separate skillet until golden and crisp, about 2-3 minutes per side.
Once crispy, transfer the bologna slices onto paper towels to drain excess fat and keep them crispy.
If adding a fried egg, crack the egg into the same skillet and cook sunny side up until the whites are set but the yolk remains runny, about 2-3 minutes.
Assemble the sandwich by placing the crispy bologna on the toasted bread, adding mustard or pickles if desired, then topping with the fried egg.
Let the sandwich sit for a minute to meld the flavors, then cut in half to reveal the crispy edges and juicy interior, ready to enjoy.
