Put the fingerling potatoes in a pot and cover with at least 2 inches of water. Salt the water heavily. Bring the pot to a simmer and cook the potatoes until almost cooked through, about 20 minutes. You should feel the faintest bit of resistance when you pierce the potatoes with a paring knife. When they've cooled completely, cut them in half lengthwise and set aside.
If using fresh peas, rinse out the pot and add fresh water about 3 inches deep. Salt heavily. Bring to a boil and add the peas. Blanch the peas until cooked through, 8 to 10 minutes. Scoop out the peas and transfer to a bowl of ice water.
In a large bowl, whisk together the creme fraiche, chives, horseradish, mustard, lemon zest, lemon juice and sugar. Set aside until ready to use.
Put the bacon strips with the olive oil in a large skillet. Turn the heat to medium. When the bacon is crisp and golden brown, about 12 minutes, remove the strips to a paper-towel-lined plate, leaving any rendered fat in the skillet. Turn up the heat to medium-high and add the halved potatoes, in a single layer, in batches. Season with salt and pepper. When the potatoes are golden brown and crisp all over, 2 to 3 minutes per batch, remove them from the skillet and transfer them directly into the bowl of creme fraiche dressing. Repeat with the remaining potatoes. Add the cooked peas (or thawed peas if using) and the snap peas. Taste and add more salt and pepper if necessary. Serve warm.
I often like to use methods other than boiling to cook my potatoes for a potato salad. Whether grilled, roasted, or browned in a skillet, the potatoes have even more flavor. In this case, cooking the potatoes in the bacon fat was a natural way to make use of the leftover fat and to amp up the flavors in this dish. The addition of peas and sugar snaps gives the salad a dose of freshness.