Make the balsamic reduction: pour 1 cup balsamic vinegar into a small saucepan and simmer over low heat, stirring occasionally, until it thickens and lightly coats a spoon, about 10–12 minutes. Remove from heat and let cool (it will thicken further as it cools).
Cook the tortellini according to package instructions until tender. Drain well and spread on a plate or tray to cool to room temperature.
Rinse and dry the cherry tomatoes, drain the ciliegine mozzarella, and pick, wash, and dry basil leaves (about 48 leaves).
Set up an assembly line with skewers or cocktail picks and the prepared ingredients.
Assemble each skewer in this order: cherry tomato, folded basil leaf, mozzarella ball, one cooked tortellini, another basil leaf, and finish with a cherry tomato. Repeat to make 24 skewers.
Arrange skewers on a serving platter, drizzle with 2–3 tablespoons balsamic reduction, and finish with a few pinches of coarse sea salt; serve.
