Position an oven rack in the top third of the oven and preheat to 190°C. Line a rimmed baking sheet with parchment paper and arrange the bacon slices in a single layer on top. Bake until the bacon is golden brown and crispy, 15 to 20 minutes, flipping once halfway through. Transfer the bacon to a paper-towel-lined plate to absorb any excess fat and let cool. Crumble cooled bacon.
Discard the parchment and pour off the remaining excess bacon drippings from the baking sheet, leaving only a thin coating of fat on the baking sheet. Reserve the poured-off drippings. Increase the oven temperature to 450 degrees F.
Toss the fingerling potatoes with 2 tablespoons of the reserved bacon drippings, 1 teaspoon salt and 1/4 teaspoon pepper. Place the potatoes cut-side-down on the baking sheet in a crowded single layer. Bake until the potatoes just start to brown, 15 minutes, then flip and continue to bake until cooked through, golden brown and crisp, about 15 minutes more.
Remove the potatoes from the oven and place the baking sheet on a heat-safe surface. Use a spatula or wooden spoon to push the potatoes together so that they are all touching but remain in a single layer. Sprinkle the potatoes with the cheese and bacon, return to the oven and bake until the cheese is melted, 2 to 4 minutes.
Transfer the potatoes to a platter with a large spatula. Top with dollops of sour cream and the spring onions. Finish by squeezing the lemon over the top. Serve hot.
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From Food Network Kitchen