Mushroom and Yellow Cheese Burger on a Bun with homemade mayonnaise

👨‍🍳 Method

For the Meatball mix

1. 1
   Shape the ground meat into 4 flat round patties 11 cm across. Press your thumb into the center of each patty so it doesn't puff up as it cooks.
2. 2
   Season the patties on all sides with salt and black pepper.

For the Fried onion

1. 3
   Heat the butter in a wide pan over medium heat.

   StoveFrying pan
2. 4
   Add the onion and fry for 10 minutes, stirring, until it is golden and tender.

   Stove

   💡Add by cooking time: what needs long (onion, carrot, meat) goes in first, and what burns fast (garlic, dry spices) goes in last, only until fragrant.
3. 5
   Add the mushrooms and fry 6 minutes, stirring, until the mushrooms release their liquid and it evaporates.

   Stove

To assemble

1. 6
   Put the egg, mustard, salt and black pepper in the blender jar and blend about half a minute.

   BlenderorStick blenderorFood processor
2. 7
   Add the oil in a thin, slow stream, while the blender is running, until a thick emulsion forms.

   Blender

   💡The thin stream is everything: fat that goes in too fast can't bind, and the sauce breaks. For mayonnaise and hollandaise, if this happens, start with a fresh yolk and slowly add the broken sauce to it; if the sauce is too thick, thin it with a teaspoon of water.
3. 8
   Add the lemon juice and stir. Taste and adjust the seasoning.
4. 9
   Mix the mayonnaise, ketchup and mustard into a smooth sauce.

   Bowl
5. 10
   Heat the heavy skillet over high heat and drizzle the olive oil over it.

   StoveFrying pan

   💡What you brown (meat, patties, schnitzel) goes into hot oil: in lukewarm oil it soaks it up and comes out greasy. For onion and garlic that you soften, oil heated over medium or low heat is enough; do not wait for it to smoke.
6. 11
   Grill the meatballs 3–4 minutes per side, until they are browned outside.

   Stove

   💡Don't press the patties with a spatula or flip them more than once: the juices run out and the patty dries out or falls apart. It releases from the pan once the underside is browned.
7. 12
   In the last minute of grilling, place a slice of cheese on each patty and cover until the cheese melts.
8. 13
   Halve the buns and toast them lightly.

   Knife
9. 14
   Spread the sauce on the buns.
10. 15
    Arrange the lettuce in each bun, and top with a hot patty and the mushroom and onion mixture.