These extra juicy, perfectly cooked French Onion Burgers are topped with melted Gruyere cheese, caramelized onions, and are served over golden burger buns.
Take part of the yellow onions and finely grate it until you have 3 Tablespoons. Set aside. (We’ll mix this into the burger meat, it makes it nice and juicy!)
Finely slice the rest of the yellow onion and the sweet onion as well. (Using a mandoline slicer makes this much easier).
In a large pot, add the sliced onions and butter. Cook, uncovered, for at least 45 minutes or until they are very brown and caramelized. Stir it occasionally as it cooks. You will have a lot of onions in the beginning, but they reduce a tremendous amount as they cook.
When the onions are nearly done, gently mix the ground beef, finely grated onions, heavy cream, and salt and pepper until just combined- don’t over-mix, you want the meat to stay nice and tender!
Mold the meat into 4 burger patties, each about ½ - ¾ inches thick. Put a thumb indentation in the middle of each one for even cooking.
Heat the 1 Tablespoon of oil in a large pan over medium heat. Cut the burger buns in half and gently place the middle sides in the oil until they are a nice golden brown. Set aside.
If needed, add an additional tablespoon of oil to the same pan and increase heat to medium-high. Don’t add the burger patties until the oil is nice and warm so that you can get a nice sear on each side.
Add the patties to the pan, you should hear a nice sizzle. Cook the patties for about 5 minutes on each side if you prefer your burgers well done. Otherwise, cook for 4 minutes on each side.
Use a wide spatula to flip each burger and add the cheese on top right away. Place a lid or aluminum foil over the pan towards the end to help the cheese melt.
Place each burger on a bun and top with the caramelized onions. Eat up!