Add one tablespoon of the 1/2 cup oil to a non-stick skillet over medium heat. Add the finely chopped onion and cook, stirring occasionally, until the onion is cooked and starting to look charred.
Add the minced garlic, salt, smoked paprika, red pepper flakes and black pepper. Cook for 1-2 minutes, until fragrant. Remove the onion mixture from the hot pan and allow it to cool.
Meanwhile, wash, dry and finely chop the parsley. I use kitchen shears to cut the curly tops from the stems. Then I wash the cut parsley in a salad spinner - so that I can spin it to dry.
In a clean bowl, mix together the chopped parsley with the cooked onion and garlic mixture, the red wine vinegar and lemon juice and the remaining olive oil. Stir until very well combined.
The sauce gets better as it sits. It will keep for 1-2 weeks in the refrigerator in an airtight container. After refrigeration, the olive oil might get solid. Just set it out to come to room temperature before serving.