Peel and thinly slice the russet potatoes. Heat olive oil in a large stockpot over medium-high heat and add potato slices, browning them slightly.

Add diced yellow onions and crushed red pepper flakes to the pot. Cook until onions are soft and translucent, then stir in minced garlic and cook until fragrant.

Pour in chicken broth, bring to a boil, then reduce heat and simmer for 10-15 minutes until potatoes are fork-tender. Meanwhile, peel and slice pepperoni, then brown in a skillet; drain on paper towels.

Use a potato masher to lightly mash the cooked potatoes until chunky. Add browned pepperoni slices.

Prepare kale by removing stems and slicing into thin strips. Add to the pot and cook for 2-3 minutes until wilted.

Season with salt to taste. Just before serving, stir in fresh lemon juice to brighten the flavors.