Caramelized Onion without ginger biscuit

itemscope itemtype="http://data-vocabulary.org/RecipeIngredient"> 2 tablespoons butter 2 onions, halved and sliced 1 teaspoon sherry vinegar 1/2 teaspoon salt[...]

2 tablespoons extra-virgin olive oil 1 medium red onion, thinly sliced 2 tablespoons balsamic vinegar 1/4 teaspoon salt 1/4 teaspoon freshly ground black[...]