Slice onions into ¼ inch slices.
Heat a wide pan or wide dutch oven to medium-high with olive oil to coat the bottom. Add the onions.
Turn the pan down to medium. Cook for 20-30 minutes before stirring. Essentially, you want to brown an entire layer of onions before stirring.
Next, flip the onions. The objective is to keep even browning and even heat on the onions.
You’ll need to flip/stir a few times more. You may need to add a couple tablespoons of water to release the fond and avoid burning.
Within an hour, your onions should be perfectly browned.
To make the Tarragon Aioli, add egg yolks, garlic, vinegar & salt to food processor. Pulse until everything is chopped and the egg is frothy.
With the food processor running, slowly add oil, until the mixture is thick.
Add minced tarragon, and salt & pepper to taste.
The easiest way is to simply remove the burgers from the box and grill. If you are pan frying them, use a high-heat oil like grape seed or peanut oil. Cook on high for a couple minutes on each side to get a nice sear.
Cut buns and brush them with clarified butter or olive oil and grill or toast to golden. Spread one side of each bun generously with aioli. Then, add the grilled burger and some caramelized onions.