It's definitely 1/2 cup. Here is the ingredients list from the blog entry last year:
1 3/4 pounds white or baking potatoes
6 tablespoons olive oil, plus more for cooking the tortilla
Salt
6 large eggs
Freshly ground black pepper
1/2 cup chives cut into 1-inch-long slices
5 garlic cloves
1/2 cup Hellmann's mayonnaise, or homemade
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1 3/4 pounds white or baking potatoes
6 tablespoons olive oil, plus more for cooking the tortilla
Salt
6 large eggs
Freshly ground black pepper
1/2 cup chives cut into 1-inch-long slices
5 garlic cloves
1/2 cup Hellmann's mayonnaise, or homemade