INGREDIENTS
2 pounds onions, sliced

7 tablespoons unsalted butter

1 cup heavy whipping cream

2 cups water

2 cups chicken stock

1 1/2 tablespoons apple cider vinegar

3 teaspoons kosher salt

2 teaspoons white pepper

parchment paper

STEPS
1) Cut your parchment paper into a cartouche -

These onions will cook for a long time, on a low heat, in order to maximize flavor. A cartouche is used in place of a lid so that the amount of moisture being released from the cooking onions can be controlled, and to prevent a skin from forming on the surface. Click HERE to watch Alex the French Guy demonstrate how to fold and cut a cartouche from parchment paper

2) Slice onions, ~1/8in - 1/4in. If you have one, use a mandolin slicer for quick and consistent results. You can reserve sliced onions in ice water to avoid crying

3) Cut the butter into 4-7 pieces, bring a large pot to medium-low heat, then add onions and butter to the pot

4) Add the salt, and cook the onions for 15 minutes. Stir often, emulsifying the butter with the water draining from the onions

5) Reduce heat to low, and place the cartouche over the onions. Cook for an additional 1 1/2 hours, stirring occasionally until your onions turn dark brown. 

6) When your onions are done, combine with heavy whipping cream, apple cider vinegar, chicken stock, white pepper, and blend smooth with a stick blender or Vitamix

7) While blending, add water until desired thickness is achieved

*You could also reserve some of the thick soup base to use as a puree under your favorite meat or vegetables.