This McDonald’s caramelized onion burger recipe hits all the right notes — melty cheddar, buttery onions, and a garlicky herb aioli on soft brioche buns. It’s not hard, just takes a little time. Worth it though. Great for weekends, or when you want real diner-style burgers at home.

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Quick Summary

Prep time: 20 mins (onions take their sweet time)
Cook time: 10–15 mins
Flavor: Buttery, savory, herby, slightly sweet
Great for: Burger nights, casual Fridays, impressive-but-not-fussy dinners

Why I Like This Recipe

I was craving something messy. One of those burgers that drips a little and makes you close your eyes on the first bite. This one’s that. The onions take a bit, but you can make ’em ahead. The rest’s fast — smash, flip, cheese, done. That aioli though? Don’t skip it. Makes the whole thing taste like you meant it.

Ingredients

For the onions:

2 medium sweet onions, thinly sliced
4 tbsp unsalted butter
Pinch of salt

For the burgers:

1 lb lean ground beef (93%)
1 tsp salt
½ tbsp high-heat oil (canola or veg)
1 tbsp butter
4 slices sharp cheddar cheese
4 brioche burger buns
Leafy lettuce (optional)

Garlic herb aioli:

½ cup mayo
2 tbsp chopped basil
2 tbsp chopped parsley
1 tbsp chopped rosemary
2 garlic cloves, minced
Fresh cracked pepper (to taste)

How To Make Caramelized Onion Burger

Caramelize your onions: Melt butter in a skillet over medium-low. Toss in the onions, salt ‘em a bit. Stir now and then for like 25–30 mins. They’ll go soft and golden. Add a pinch of sugar if you’re impatient.
Make the aioli: Whisk everything in a bowl. Let it chill while the onions do their thing. This stuff lasts days in the fridge.
Shape the burgers: Split the beef into 4. Roll into loose balls — don’t press yet.
Smash + sear: Heat a cast iron pan till it’s mad hot (5–10 mins). Brush with oil. Add a bit of butter and immediately press a beef ball flat with a spatula or jar. Season. Flip after 2–3 mins. Add cheese. Cook another 2 mins.
Assemble it: Buns toasted? Good. Spread aioli, add lettuce, then the cheesy patty. Pile on those onions. Done.

Tips for Success

Make the onions ahead if you’re short on time — they reheat fine.
Don’t smash the patties more than once or twice — it’s about that crust.
Use high-heat oil — butter alone will burn.
Sharp cheddar adds bite — don’t sub with boring cheese.

Storage and Reheating

Fridge: Store leftover onions and aioli separately. Burgers reheat best unassembled.
Microwave: Eh. Will work, just wrap the patty in a damp paper towel — 30–45 secs.
Skillet (best): Reheat patty in a hot skillet with a lid for 1–2 mins. Keeps the crust.
Don’t freeze assembled burgers — it’s not that kind of meal.

Frequently Asked Questions

Can I use a different kind of onion?
Yeah, but sweet onions caramelize best. Reds get weird.
Do I have to toast the buns?
Technically no. But toasted = better texture, holds the sauce.
Can I grill instead of using a skillet?
Sort of. You’ll lose the smash effect unless you use a flat griddle on the grill.
How long does the aioli last?
Up to 4–5 days in the fridge. Great on sandwiches too.
Is it super greasy?
Honestly? A little. But in the good way. Use paper towels if needed.

Common Mistakes and How to Dodge Them

1Rushing the onions: You can’t. Low and slow or don’t bother. Add sugar if you need to speed up but don’t burn them.
Over-smashing the burgers: Smash once, maybe twice — early on. Pressing too much ruins the sear and makes ’em dry.
Skipping the rest time for patties: Let them sit off heat for a minute before assembling. Keeps juices in.
Cheese timing off: Add cheese right after the flip. Don’t wait or it won’t melt properly.
Skipping the aioli: It’s literally the best part. Don’t bail and just use ketchup. Please.

Nutrition Facts (Per Burger – Approximate)

Calories: ~610
Total Fat: 38g
Saturated Fat: 15g
Cholesterol: 105mg
Sodium: 750mg
Potassium: 380mg
Total Carbohydrate: 28g
Dietary Fiber: 2g
Sugars: 6g
Protein: 32g