How to Make It
Melt 1 tablespoon of the butter in a large saucepan. Add the onions and shallots and cook over moderate heat, stirring, until softened but not browned, about 8 minutes. Season with salt and pepper. Add the flour and cook, stirring, for 1 minute. Whisk in 1/2 cup of the wine until smooth, then gradually whisk in the remaining wine.
In a square of cheesecloth, combine the juniper, parsley, thyme and bay leaf and tie with string. Add the herb bundle to the pan and simmer over low heat, skimming, until the wine has reduced to 1 1/2 cups, about 45 minutes. Pass the sauce through a coarse strainer.
Meanwhile, melt 2 tablespoons of the butter in a large skillet. Add the pancetta and cook over moderately low heat until lightly crisped, about 4 minutes. Add the mushrooms, season with salt and pepper and cook over high heat, stirring occasionally, until lightly browned, about 8 minutes. Add the port and boil until almost evaporated, about 2 minutes. Stir in the wine sauce and simmer for 1 to 2 minutes. Remove the skillet from the heat and swirl in 1 tablespoon of butter, then season with salt and pepper.
In a large skillet, melt the remaining 2 tablespoons of butter in the oil. Add the bread and cook over moderately high heat until browned, about 2 minutes per side. Drain on paper towels.
Fill a large skillet with enough water to reach two-thirds of the way up the side. Add the vinegar and bring to a boil. One at a time, break the eggs into the bubbling water. Regulate the heat so the water barely simmers and poach the eggs until the whites are set but the yolks are still soft, 3 to 4 minutes. Using a slotted spoon, transfer the eggs to paper towels.
Gently reheat the sauce and spoon it into soup plates. Add 2 bread triangles to each plate and set an egg on top of each triangle. Garnish with chives; serve hot.