How to Make It
Preheat the oven to 300°. Butter four 1-cup ramekins. In a large skillet, melt the butter. Add the bacon and cook over moderate heat until lightly browned, about 4 minutes. With a slotted spoon, transfer the bacon to a plate. Add the chicken livers to the skillet, season with salt and white pepper and cook over moderate heat until browned, about 2 minutes per side. Transfer to the plate.
Add the onion, apple and allspice to the skillet and cook over low heat, stirring occasionally, until the onion and apple are softened, about 5 minutes. Add the Calvados and carefully ignite it with a long match. When the flames subside, scrape the apple-onion mixture into a blender and let cool to room temperature.
Add the bacon and chicken livers to the onion-and-apple mixture in the blender, along with the half-and-half, egg yolks and 1 teaspoon of kosher salt. Blend until very smooth. Pass the mixture through a coarse sieve into a large glass measuring cup. Pour into the prepared ramekins and transfer to a small roasting pan. Add enough hot water to reach halfway up the sides of the ramekins, cover loosely with foil and bake the chicken-liver mousse for about 1 1/2 hours, until an instant-read thermometer inserted in the mousse registers 155°. Remove the ramekins from the water bath and let cool to room temperature.
Cover and refrigerate the ramekins until the mousse is chilled, preferably overnight. Serve with toasted baguette slices and Pickled Red Onion.