Heat a griddle or cast-iron skillet over medium heat. Lay the bacon strips flat and cook until crisp, letting the fat slowly render out—don’t rush this over high heat. Once done, transfer the bacon to a paper towel-lined plate. Reserve the bacon grease in the pan for the next steps.
Add sliced onions directly into the pan with the hot bacon grease. Sauté over medium heat, stirring occasionally, until the onions soften and begin to caramelize—about 5 to 7 minutes. If the pan looks dry, add a touch of butter to help them along. You’re not going full caramelization here, just a quick cook to bring out that sweet, savory flavor.
In a small bowl, mix your softened butter with 1–2 tablespoons of the reserved bacon grease. Spread this mixture on one side of each slice of bread. This is your secret weapon for a crispy, flavorful golden crust.
Turn the heat to medium-low. Lay one slice of bread, buttered side down, onto the griddle. Layer with cheese, bacon, pulled pork, a light drizzle of BBQ sauce, and a spoonful of sautéed onions. Top with the second slice of bread, buttered side facing up.
Cook the sandwich until the bottom is golden brown and crispy, about 3–5 minutes. Carefully flip it, press lightly with a spatula, and cook the other side until crisp and the cheese is fully melted. If the bread starts to brown too quickly, reduce the heat to low or move it to indirect heat on your grill setup.
Once the sandwich is crisped to perfection and the cheese is melted , remove it from heat, slice diagonally, and serve hot. Add extra BBQ sauce or slaw on the side if you're feeling fancy.