In a medium saucepan, combine 1 cup of blueberries, 1/4 cup of white sugar, and the juice of half a lemon along with a sprig of lemon thyme. Heat over medium-high until the mixture comes to a boil; then reduce the heat and let it simmer for about 15–20 minutes. Stir occasionally until it thickens to a jam-like consistency and is bursting with sweet and tart flavor. Allow the compote to cool before using.

Take two slices of your chosen thick-cut bread and spread a generous layer of the cooled blueberry compote on one side of each slice. Sprinkle an equal amount of shredded white cheddar and mozzarella cheese on top of the compote layer. Top with the remaining slices of bread, compote side down, to form two sandwiches.

Heat a cast-iron skillet over medium-low heat. Spread softened butter on the outer sides of each sandwich. Place the sandwiches in the skillet and cover. Grill for 2–3 minutes until golden brown and crispy, then flip carefully.

Continue to grill for another 2–3 minutes, ensuring the cheese melts thoroughly. Adjust the heat if the bread browns too quickly.

Once the sandwiches are golden and the cheese is melted, remove them from the skillet. Let them rest for a minute before cutting in half diagonally. Garnish with flaky sea salt and fresh lemon thyme.