Preheat oven at 200°C/390°F. Line 1 or 2 baking sheets with parchment paper.
Remove and discard the ribs. Tear the leaves into pieces and place them in a bowl, add olive oil and season well with salt. Mix with your hands until evenly coated. Spread them out on the prepared baking sheets, without overlapping (or they will not be crispy).
Bake for 5 minutes, then carefully flip them over and bake for 2-3 more minutes, or until crispy. Remove from the oven and add 1 tbsp olive oil, a few drops of vinegar and toss to coat.