In a large sauté pan, melt the Butter (2 tablespoon) over medium heat. Add the Onion (4 cup), Kosher Salt (to taste), and cover the pan. Cook covered for about fifteen minutes.
Remove the cover, and increase the heat slightly. Continue to cook for another ten minutes.
Sprinkle the Granulated Sugar (1/2 teaspoon) on top and cook for another ten to fifteen minutes. stirring more frequently now, until the onions have turned a nice deep brown.
Pour in the Distilled White Vinegar (1/2 teaspoon) turn off the heat, and scrape the bottom of the pan with a wooden spoon or spatula to remove any browned bits. Take pan off the heat and transfer onions to a large bowl to cool.
When the onions have cooled, stir in the Sour Cream (1/2 cup). Season with Salt and Pepper (to taste).
Fold in Scallion (4). Add the Lemon Juice (1/2 teaspoon). Taste and adjust seasoning as desired.