In a non-reactive saucepan, combine the Champagne vinegar, water, sugar, black peppercorns, and chili flakes. Bring to a boil, season with salt and pepper, and add the cleaned fiddlehead ferns. Simmer gently until the fiddleheads are tender but not mushy (retaining a crunch), about 25 minutes. Remove from heat and allow to cool completely. The fiddleheads can be prepared ahead of time and kept for about a month in the refrigerator.
In a double boiler, combine the pecorino, fontina, milk, and heavy cream. Whisk constantly, allowing the mixture to melt until it is creamy and lump free. One at a time, add the egg yolks until they are fully incorporated. Whisk constantly, the agitation will prevent the eggs from curdling. After 3-4 minutes, the sauce should begin to thicken. Remove from the heat and whisk for another minute or two. When the mixture becomes a thick, creamy sauce, remove from heat and keep in a warm place.
At the restaurant, we cook ramps bulb side down on the edge of the piastra (or flat top). At home, ramps can be grilled or even roasted. Season with olive oil and pepper and allow the bulbs to char, turning frequently until they are tender all the way through. Flip the ramps so that the leaves are in contact with the heat source and allow to wilt just barely. (Be careful not to over cook or char the leaves because they become bitter. They should be just barely wilted.)
Remove the ramps from the heat and allow to cool slightly. When cool enough to handle, coarsely chop the ramps into 1/4-inch lengths. Toss with salt, pepper, lemon juice and olive oil.
Lightly toast the bread, then spoon the charred, seasoned ramps on top of each slice. Top with the pickled fiddlehead ferns and drizzle with the fonduta.