The mellow, nutty flavour of roasted garlic is quite different from the spicy pungency of fresh garlic. This vinaigrette is delicious on mixed salad. You can make it ahead and keep it in the fridge in a jar - just shake before using.
Preheat the oven to 180 C / Gas 4. Rub 1 teaspoon of the olive oil over the garlic bulb and wrap it in aluminium foil.
Bake garlic in the preheated oven until soft, about 40 minutes. Remove to cool.
Meanwhile, whisk together the remaining olive oil, balsamic vinegar, Dijon mustard and caster sugar in a small bowl. When the roasted garlic is cool enough to handle, squeeze 3 or 4 cloves of the roasted garlic (or more, according to your taste) into the vinaigrette. Season with salt and pepper. Reserve the remaining roasted garlic for another use.