If not already done, slice your Irish soda bread into approximately 1/2-inch thick pieces. Grate or thinly slice the sharp cheddar cheese. Finely chop the fresh chives. Have your softened butter ready.

Lightly spread one side of each soda bread slice with softened butter. These will be the exterior sides of your grilled cheese sandwiches. Flip two of the bread slices over so the unbuttered side is facing up.

If using, spread 1/2 tsp of Dijon mustard thinly over the unbuttered side of these two slices. Layer half of the sharp cheddar cheese evenly over the mustard (or directly on the bread if omitting mustard). Sprinkle half of the chopped chives over the cheese. Add a pinch of salt and pepper.

Repeat with the remaining cheese, chives, salt, and pepper on the second sandwich. Place the remaining two buttered bread slices on top, butter-side-up, to complete your two sandwiches.

Preheat a large skillet or griddle over medium-low heat. This lower heat is crucial for ensuring the cheese melts completely before the bread burns.

Carefully place the assembled sandwiches into the warm skillet. Cook for 5-7 minutes per side, or until the bread is golden brown and crispy, and the cheese is thoroughly melted and gooey. You may need to adjust the heat slightly to prevent burning. If the bread is browning too quickly, reduce the heat.

Use a spatula to gently press down on the sandwiches occasionally while cooking to ensure even contact with the pan and help with browning and melting.

Once cooked, remove the Irish soda bread grilled cheese sandwiches from the skillet. Let them rest for a minute on a cutting board, then slice them diagonally. Serve immediately with your favorite soup or a fresh side salad.