1/2 cup whole peeled hazelnuts
6 tablespoons extra virgin olive oil (EVOO), divided
1 large onion, finely chopped
Salt and pepper
3 tablespoons balsamic vinegar, divided (eyeball it)
1/2 tablespoon Dijon mustard
3 plum tomatoes, sliced
4 large cups baby spinach, arugula or a different green of your choice
1/4 cup blue cheese crumble
Pre-heat the oven to 325°F. Place hazelnuts on a baking sheet and put them in the oven to toast them up, about 10-12 minutes – your nose will know when they are done. Remove them from the oven and cool. Run your knife through them once, chopping them coarsely. While the nuts are toasting, place a large skillet over medium-high heat with two turns of the pan of EVOO, about two tablespoons. Add the onion, season with a little salt and pepper and cook, stirring frequently, for 10 minutes. Add one tablespoon of the balsamic vinegar and a big splash of water. Use a wooden spoon to scrape up any bits on the bottom of the pan and cook for about one minute.
Remove the onion from the skillet and transfer to a bowl. Add remaining vinegar and mustard to the bowl and whisk in remaining EVOO in a slow, steady steam.
In a salad bowl, combine the tomatoes, greens, cooled hazelnuts and the blue cheese crumble. Pour the caramelized onion dressing over the salad and toss to coat. Adjust the salt and pepper to taste.