Place the cleaned mussels, still in their shells, in a large saucepan with ½ cup wine over high heat. Cover and let cook until the mussels open up and release their juices, about 3 minutes.


Drain, reserving all the strained mussel liquid. Remove the mussels from their shells and discard the shells.


Cut the onion into 1/8 inch thick half-moons. In a 2-quart saucepan, heat the olive oil over medium heat. Add the garlic, hot chili pepper and the onions, cooking until soft and golden brown, about 8 to 10 minutes. Add wine, bring to a boil and cook 1 minute.  Add the mussels to the saucepan, and then add the black pepper and the reserved mussel juices. Raise the heat to high and allow the mussel mixture to boil for 30 seconds.


Remove the pan from the heat, add the chopped parsley, the agretti, a pinch of hot chili pepper and a drizzle of extra-virgin olive oil. Place 2 crostini on the bottom of 4 plates and divide the mussels and sauce among the bowls and serve.