Slow Cooker French Onion Soup

Onion soup might seem a bit strange for the beach, but the Catnap is a year-round kind of place. This recipe is probably a bit better for our Fall, Winter, and Spring (it is that time of year) guests than for those in the Summer.

This is a delicious result from a low-intensity effort and amazingly little work. One starts the cooking in the evening and enjoys the results for dinner the next day with very little muss and fuss.

Note: The Catnap is equipped with a small crock pot but this recipe was tested with our larger one at home so check the size before proceeding and adjust the recipe if necessary! When you get to the “Add the beef stock …” step, it’s TOO LATE.


  • 3 pounds yellow onions (three really big ones or more smaller ones)
  • 2 tablespoons unsalted butter
  • 2 tablespoons olive oil
  • 1 teaspoon sea salt
  • 1 ½ teaspoon coarse ground black pepper
  • 2 tablespoons balsamic vinegar
  • 10 cups (2 ½ quarts) beef stock
  • 1 beef bullion cube
  • 3 tablespoons cognac
  • 1 to 2 baguette slices per bowl
  • 1/3 cup Gruyere cheese per bowl
  • 1 tablespoon Parmesan cheese per bowl

Very easy soup instructions:

  • Peel the onions and cut them into chunks (they don’t have to be particularly small)
  • Season the onions with the salt and pepper
  • Put the onion chunks, butter, and olive oil the slow cooker (check beforehand to verify that it’s big enough)
  • Cook on LOW (about a 215 degree cooking, not warming, setting) overnight (about 12 hours), the onions should end up soft and golden brown
  • Add the beef stock, bullion cube, balsamic vinegar, and cognac and stir the result
  • Ignore the pot for another 6 to 8 hours on the same LOW setting (you can go longer, just watch the water level)
  • After a few hours, taste the soup and add any seasonings it seems to lack

Very easy (but fancy looking) serving instructions:

  • You need one oven-safe bowl per person
  • Preheat the oven to 350°F
  • While the oven is heating, slice the baguette so that you have enough sliced bread to more or less cover the soup in the bowls
  • Toast the bread
  • Put soup into the bowls and put the bowls in a baking pan for easy handling and spill control
  • Top each bowl with toast and a generous quantity of Gruyere cheese, then garnish with Parmesan
  • Bake for 20 minutes or so with the rack in the upper third of the oven (the cheese should be completely melted)

Being very careful because the bowls are HOT, let them cool for several minutes before placing them on appropriate mats in front of the diners! (The test case showed that this is actually a really good idea, even with mature adults)

Did I mention that the bowls will be HOT? Be careful.

A couple things from the recipe that I used to develop this one but didn’t test:

  • Switching the oven to broil for 2 minutes or so can bring the cheese to a golden brown if you want (the test case did not need this)
  • You can garnish the cheese covered soup before serving using some parsley or chopped scallion or onion