In a large pot of boiling salted water, blanch the fiddleheads until they are crisp- tender. Remove the fiddleheads from the water and shock them in a bowl of ice water (unless you are going to use them immediately). While the fiddleheads are cooking, heat the butter in a medium saute pan. Add the shallots and the peppers, cooking for 2 minutes. As you remove the fiddleheads from the water, drain them well and place in the pan with the shallots and peppers. Add the thyme, salt and white pepper. Heat through and serve them up in a pretty bowl.