Step-by-Step Instructions
Step 1: Prepare the Bread
In a small bowl, combine the softened butter and mayonnaise if using, mixing until well blended. Spread this mixture evenly and generously across one side of each bread slice, covering the surface all the way to the edges. Even coverage is important — any unbuttered areas will brown unevenly and produce pale, soft patches in the finished crust. If you are using butter only without mayo, make sure it is properly softened at room temperature, as attempting to spread cold butter tears the bread and creates uneven distribution. Set the prepared bread slices aside.
Step 2: Assemble the Sandwich
Place one slice of bread on your work surface with the buttered side facing down. Distribute the grated cheeses evenly across the unbuttered surface, mixing the two types together or layering them — either approach works equally well. Keep the cheese slightly inset from the edges of the bread by about a quarter inch on all sides; a small amount of cheese leakage during cooking is normal and actually produces delicious crispy cheese bits around the edges of the finished sandwich, but too much overhang results in cheese burning in the pan and a messy result. Place the second slice of bread on top with the buttered side facing upward.
Step 3: Heat the Pan Correctly
Place a heavy-bottomed skillet — cast iron is ideal, but any heavy non-stick pan works — over medium-low heat. Allow it to heat for a full minute before adding the sandwich. This preheating step is important: a cold pan produces uneven cooking, while a pan that is too hot will burn the bread before the cheese has had time to melt. The correct temperature range for grilled cheese is medium-low to low — patient enough for the cheese to fully melt while the bread crisps, rather than aggressive enough to toast the outside before the center is molten. If you see the bread browning rapidly within the first 30 seconds of cooking, your heat is too high and should be reduced immediately.
