Naranjas agrias, brought to the New World by Spaniards, are bitter and have a thicker skin than their sweeter sisters. Their color can vary from orange to yellow to pale green and they give off a very distinctive scent. If you cannot find sour oranges, replace the juice in recipe with juice from two regular oranges and two lemons.
1 tbsp. Dijon mustard
Juice of 2 sour oranges
Juice of 1 orange
1/2 tsp. fine sea or kosher salt
1 cup olive oil
1 garlic clove, crushed
1/2 small red onion, chopped fine
Whisk mustard with citrus juices until combined. Stir in salt. Gradually whisk in olive oil until dressing is combined. Add garlic clove and chill. Remove garlic clove and add red onion.