In saucepan, over medium heat, bring balsamic vinegar to a boil. Reduce heat and simmer for 10-15 minutes, or until reduced to ½ cup (125mL). It will thicken as it cools.
In a bowl, whisk together reduced vinegar, mustard, garlic, salt and pepper. Slowly drizzle in oil, whisking to combine.
Trim basil leaf if necessary, and wrap each boconccini. Skewer wrapped cheese and one grape tomato (alternate red and yellow tomatoes if using, for contrast).
Serve with dipping sauce.