1. In a large pot, bring potatoes to a boil in salted water over high, then reduce to a rapid simmer. Add leek and kale and cook until potatoes are tender when pierced with a knife, about 10 minutes. Drain;transfer to a large bowl.

2. In a large cast-iron or nonstick skillet, cook bacon over medium-high until crisp, 8 to 10 minutres. With slotted spoon, transfer to bowl with vegetables. Season with salt and pepper. With fork, mash potato mixture until few lumps remain. With your hands, form into 12 patties.

3. Pour off fat from skillet and wipe clean, add butter and melt over medium. In batches, cook cakes until golden on both sides, about 6 minutes, flipping once.