How to Make It
Trim the chicken livers of any sinews and veins and set them on paper towels to dry for about 20 minutes.
Preheat the oven to 350°. In a large skillet, melt the butter in 1 tablespoon of the olive oil. Add the chopped onion, sage and rosemary and cook over moderately high heat, stirring occasionally, until the onion is softened, about 5 minutes. Stir in the minced anchovy and capers and cook over low heat until the onion is lightly browned, about 8 minutes longer. Scrape the mixture into a medium bowl.
Add the remaining 3 tablespoons of olive oil to the skillet. Season the chicken livers with salt and pepper, add them to the skillet and cook over high heat until browned, about 2 minutes. Flip and cook the chicken livers for 1 minute longer. Stir in the onion mixture. Add the cognac and carefully ignite it with a long match. Cook the livers until the flames subside.
Discard the herb sprigs and scrape the contents of the skillet into a food processor; let cool slightly. Pulse until chunky, then season with salt and pepper.
Place the baguette slices on a large baking sheet and toast them for about 15 minutes, until they are golden and crisp. Spread the baguette toasts with the chicken liver and serve.