Wash the chicken livers and get rid of any stringy membrane. Melt a large knob of butter in a large frying pan and add the livers. Fry over high heat until browned but still pink in the middle – about 3 minutes. Transfer to a food processor.
Add more butter to the frying pan and add the onions and thyme leaves. Cook over medium heat until soft. Add the garlic and cook for 2 minutes. Transfer to the food processor. Deglaze the frying pan with the brandy and soy sauce. Scrape all the bits into the food processor.
Add the ground hazelnuts to the food processor and blend until smooth. Allow to cool for a few minutes and then add most of the remaining butter. Process until well blended and season to taste with salt and ground black pepper. Spoon the pate into a mould or terrine and tap to get rid of air bubbles. Cover with a layer of melted butter to stop the liver from getting bitter. Garnish with a grinding of black pepper and sprigs of thyme. Serve with toast or crostini.