Carefully remove the skin, tendons, and green bile sacs from the chicken livers (½ kg total). Rinse them under cold water and pat dry.
In a bowl, mix the paprika powder, crushed garlic, salt, and black pepper. Add the cleaned chicken livers and toss thoroughly to coat evenly with the spice mixture. If not cooking immediately, cover and refrigerate.
Heat 50 g of butter in a large pan over medium-high heat until very hot. Add the spiced livers and stir vigorously continuously, cooking until browned all over, about 3-4 minutes. Transfer the cooked livers to a preheated bowl and set aside.
Add the finely chopped onion to the same pan and sauté over low heat for about 2-3 minutes until softened. Increase the heat to medium-high, add the sherry and sugar, and simmer until the sherry is almost completely reduced, about 2-3 minutes.
Pour the chicken broth into the pan, stir well, and simmer over medium heat until reduced by half, about 5-7 minutes. Gradually add the remaining 50 g of butter in small pieces, swirling the pan gently after each addition until completely dissolved. Season to taste with salt and pepper. Pour the sauce over the cooked livers and serve in a large bowl or individual bowls.