Crush the walnuts into bite-sized pieces. If unavailable, substitute with almonds.

In a pan, combine sugar, water, and a pinch of salt. Boil until the sugar dissolves completely without stirring.

Add the walnuts to the syrup and simmer until well-coated and caramelized.

Heat butter in a pan and toast both sides of the bread slices until golden brown.

Place one slice of cheddar cheese on a toasted bread slice, followed by the caramelized walnuts, mozzarella cheese, and another slice of cheddar cheese.

Top with another slice of bread and toast on low heat until the cheese melts.