How to Make It
Preheat the oven to 425°. Wrap the garlic cloves in foil and set on a rimmed baking sheet. Brush the onions with oil and arrange on the baking sheet. Bake for about 1 hour, until the onions and garlic are lightly charred and soft. Let cool.
Peel the garlic and transfer the cloves to a blender. Add the onions, cider vinegar and lemon juice and puree until smooth. With the blender on, gradually add the 1 1/4 cups of vegetable oil until incorporated. Season the dressing with salt and pepper.
In a large bowl, toss the lettuces with 1/2 cup of the dressing and season with salt and pepper. Transfer to a serving bowl or platter. Arrange the remaining ingredients on top and serve, passing the remaining dressing at the table.