Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Dice potatoes into 1/2-inch pieces. Halve, peel, and dice onions. Trim and thinly slice scallions, separating whites from greens. Halve lemon. Drain and rinse corn.

Heat a medium pan over medium-high heat. Add bacon and cook, flipping, until crisp, 8-10 minutes. Transfer to a paper-towel-lined plate. Place naan on a baking sheet; drizzle with olive oil and season with salt and pepper. Bake on top rack until crisp, 6-8 minutes. Halve naan.

Melt 2 TBSP butter in a large pot over medium-high heat. Add onions and scallion whites. Cook, stirring, until softened, 4-5 minutes. Season generously with salt and pepper. Stir in flour and cook 1 minute. Slowly pour in milk, a little at a time, until completely incorporated.

Stir potatoes, stock concentrates, and 21/2 cups water into pot. Season with plenty of pepper. Bring to a boil, then lower heat and reduce to a simmer. Cook until potatoes are tender and easily pierced by a knife, about 15 minutes.

Once potatoes are tender, lightly mash in pot with a potato masher until chunky—some pieces should be crushed, but a few whole ones should still remain. Stir in corn and allow to warm through. Stir in half the sour cream. Taste and season with plenty of salt and pepper. TIP: Add a splash of water if soup is very thick.

Place lettuce and cranberries in a large bowl. Add a squeeze or two of lemon juice and 21/2 TBSP olive oil. Season with salt and pepper; toss to combine. Crumble bacon. Divide soup between bowls. Dollop with remaining sour cream. Sprinkle with cheddar, bacon, and scallion greens. Serve with naan for dipping and salad on the side.