01 - Heat a skillet or grill pan over medium heat.
02 - Spread softened butter evenly on one side of each slice of sourdough bread.
03 - On the unbuttered side of two bread slices, arrange the fresh mozzarella slices, followed by the halved cherry tomatoes, and then the fresh basil leaves. Drizzle with 10 ml (2 teaspoons) of balsamic glaze and season with salt and freshly ground black pepper.
04 - Place the remaining two bread slices on top of the assembled layers, ensuring the buttered side of each is facing outwards.
05 - Carefully place the assembled sandwiches into the preheated skillet. Cook for 3 to 4 minutes per side, gently pressing down with a spatula, until the bread achieves a golden-brown crispness and the mozzarella is fully melted.
06 - Remove the grilled cheese from the skillet and allow it to rest for 1 minute. Slice in half and serve warm. Drizzle with additional balsamic glaze if desired.