How to Make It
In a large skillet, melt 4 tablespoons of the softened butter. Add the shallots and cook over moderately low heat, stirring occasionally, until softened, about 8 minutes. Add the chicken livers, season with salt and pepper and cook over moderate heat, turning a few times, until firm, about 4 minutes. Add the Marsala and simmer for 2 minutes. Add the chicken stock and simmer, turning the livers a few times, until the livers are light pink in the center, about 6 minutes. Remove from the heat and let the skillet mixture cool for 5 minutes.
Transfer 10 of the livers to a plate. Transfer the contents of the skillet to a blender and puree. Cut the remaining 1 1/2 sticks of softened butter into tablespoons. With the machine on, add the butter and blend until it is completely incorporated.
Scrape the puree into a large bowl. Cut the reserved 10 livers into 1/2-inch pieces and fold them in, along with the whole pistachios, parsley and thyme. Generously season the pâté with salt and pepper. Spoon the pâté into four 1 1/2-cup ramekins. Cover with plastic wrap and refrigerate until firm, about 2 hours.
Pour 1 tablespoon of the melted butter over each pâté to seal it, then garnish with the chopped pistachios. Cover the ramekins and refrigerate until the butter is firm, about 20 minutes.