* Make sure to add the butter; I forgot to mention that in the video I made!
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Here’s the recipe in text form:
- Set out a cutting board and, next to it, a large microwave-safe container for sliced onions. Add 4 tablespoons (60g) of butter to the container.
- Slice 4–6 large yellow onions, about 2 pounds (900g). Start by cutting the root and stem ends off, slicing in half (top to bottom), and then peeling off the skin. Make sure to remove any tough outer layer, as it’ll end up in your soup. Chop the onion halves into slices, transferring to the container as needed to free up space on your cutting board.
- Now for the unorthodox part. Cooking onions on the stovetop is a thermal balancing act between getting the stove hot enough to simmer the onions in their own liquid but keeping it cool enough to not dry them out and burn them. Microwaving onions may sound crazy, but it nails this balancing act perfectly: the microwave heats the water in the onions, causing them to simmer, but doesn’t excite the drier parts and thus doesn’t burn them. It still takes as long—30 to 45 minutes—but it’s astonishingly simple.
- Microwave the onions and butter for 15 minutes on high power, then stir them together. The onions should be translucent and wilted at this point, but not brown. Fetch out any bits of onion skin that accidentally made it in while you’re at it. Nuke for another 15 minutes. Stir again, and again fetch out any bits of onion skin that somehow made it in. The onions should be getting smaller in volume at this point, and perhaps beginning to turn brown. Microwave for additional 5-minute intervals until the onions have reduced way down and are mahogany brown.
- Transfer the onions to a pot and stir in 1 quart (~1 liter) unsalted vegetable stock; 2 tablespoons (30 mL) brandy, whiskey, or sherry (optional, but adds a very nice depth; use sherry if you like the sweetness); and 1 teaspoon (6g) salt Freshly ground pepper.
- Taste and adjust the seasoning as desired, taking care to not oversalt the liquid as the cheese will balance that out. You can store the soup at this point for several days in the fridge.
To serve, bring the soup to a simmer. Ladle it into oven-safe soup bowls (or a shallow oven-safe pan, if you’re serving family-style) and cover it with slices of dried, toasted bread. (Do not skip drying and toasting the bread; you will end up with soggy wet goo. You can use stale bread and toast it; otherwise, dry the slices of bread out in a 300°F / 150°C oven and then toast them.
- Cover the bread with a generous layer of sliced cheese that melts well, such as Gruyère, Fontina, or Emmental, creating a layer of 1/8” / 0.5 cm cheese slices across the entire top.
- Melt and toast the cheese under a broiler, cooking it until a few spots are just on the verge of burning.