Add the butter to a larger heavy skillet.Heat the skillet over medium-high heat. Add the onions, 3/4 teaspoon salt and 1/4 teaspoon pepper. Fry the onions, flipping them now and then, until they're dark on the edges, even black and crispy in spots, about 10 minutes. Add the honey and garlic and cook for 1 more minute. Add the vermouth, bring to a simmer and cook until the liquid thickens, about 3 minutes. Remove from the heat and let cool.
Put the sour cream and cream cheese in a mixing bowl and mix with a rubber spatula until smooth. Finely chop the fried onions on a cutting board and add them, along with their pan juices, to the cream cheese mixture. Stir in the chives. Add the cayenne and season with salt.
Transfer to a small bowl and garnish with more chives. (This can be made ahead of time and refrigerated.)