Melt butter in a heavy-bottomed pot over medium-low heat. Add shallots, bouquet garni, black peppercorns and salt. While stirring frequently, sauté until shallots just begin to caramelize but don’t turn completely golden, about 15 minutes.
Increase heat to medium-high, add cabernet and Madeira and simmer until reduced by half. Incorporate stocks and simmer for 20 minutes. Add vinegar and season with additional salt and fresh ground black pepper to taste. Remove from heat, discard the bouquet garni, and stir in Cognac.
Arrange baguette slices on a sheet pan, place under the broiler and toast until golden, flipping once so both sides are toasted. Top each with a slice of triple cream.
Serve soup in bowls topped with a crouton and garnish with marjoram, thyme and thinly sliced truffle.