Leave the chicken livers marinating in the wine for 12 hours mixing occasionally. Drain the livers, keeping the wine marinade to one side. In a high sided saucepan, slowly cook the onions in the oil with salt and pepper until pale golden.
Add the chicken livers and sage and cook for 10 minutes until the livers are browned. Pour in the wine and reduce.
Continue cooking, adding small amounts of water or broth from time to time, for another 20 minutes.
Draw off the pan from the stove and add the capers and anchovies. Blend all together with an immersion liquidizer. Taste for extra salt or pepper, mix in the butter, and your patè is ready to serve.