Turn on oven to 400 degrees Fahrenheit. While oven is heating, wrap 4 cloves of garlic in aluminum foil and place on top shelf of oven (or put in small baking dish before putting in oven) for 15 to 20 minutes, until soft. Let cool to room temperature.
Combine the zest, juice, garlic, mustard, rosemary and salt and pepper in a blender (I use an immersion blendeand blend until smooth. With the motor running, slowly add the extra-virgin olive oil and blend until emulsified.
Notes
Dressing can be made 1 day in advance and refrigerated. Bring to room temperature before using.