Slice open cherry tomatoes from the rounded end (not the stem end).
Carefully scoop out the inside and place upside down on paper towel to drain.
Place feta cheese in each tomato and spoon a little balsamic vinaigrette in each one.
Garnish with a side slice of black olive.
In a bowl, mix the garlic and Dijon mustard.
Whisk this mixture with vinegar.
Slowly and steadily add the oil, whisking constantly until dressing is creamy and thickened and all the oil has been incorporated.
Taste and correct seasoning with salt and pepper.
Let stand at room temperature until you need it.