Preheat the grill or broiler.
In a 10 to 12-inch saute pan, heat the olive oil slowly over medium heat. Add the onion and cook slowly until soft, but not brown, about 10 minutes. Add the livers, capers, anchovies, and red pepper flakes, and cook until lightly browned, about 8 minutes. Add the wine and cook until only 3 to 4 tablespoons of liquid remain, about 8 minutes.
Transfer the liver mixture to a food processor and pulse on and off until blended but still lumpy -- it should not be smooth like a puree. Season to taste with salt and pepper and remove to a small mixing bowl.
Grill or toast the bread on both sides and spread each piece with 1 heaping tablespoon of the liver mixture. Divide among 6 to 8 plates and serve immediately.