Bring a pot of water to a boil and season it well with salt (a few tablespoons). Add your kale and blanch for two minutes, then use tongs to remove it to a bowl to cool before chopping it up. Set aside.
In that same pot of water (I’m saving you a dish), add your single carrot, celery stalk, and 1/2 yellow onion, plus the lentils. Lower to a simmer and cook until the lentils are just al dente, 15 to 20 minutes. Drain, discard the vegetables, and set the lentils aside.
In a large pan or Dutch oven, heat the olive oil with the pancetta over medium-high heat until very hot and the pancetta starts to render. Allow it to cook until the pancetta is crisp and has released most of its fat, 4 to 5 minutes.
Remove the pancetta to a plate and add the chopped carrot and celery and the diced onion. Sprinkle with the red pepper flakes and the maple sugar; cook, stirring, for 1 to 2 minutes.
Add the tomatoes, fry for a minute, then add the anchovies and the garlic. Cook until the anchovies dissolve and the garlic just starts to brown, another 2 minutes or so.
Pat the lentils dry and add them to the pan, frying them in the hot oil until they start to crisp up a bit, 3 to 4 minutes.
Add the pancetta and the kale and cook, stirring, for another 2 minutes. If the lentils are getting too brown, you can add some water at this point.
Taste for seasoning, squeeze the lemon juice over everything, and drizzle with the finishing oil. Serve hot.