In a large bowl, roughly mash the drained cannellini beans with a fork, leaving some texture.
Stir in the finely chopped, squeezed-dry kale and set aside.
Place a deep skillet over medium heat and add 2 tablespoons (30 ml / 1 fl oz) of the oil or butter.
Once hot, add the grated sweet potato, sprinkle with salt and pepper, and cook, stirring frequently, until it softens and begins to color, about 5 minutes.
Stir the bread crumbs, cinnamon, nutmeg, and cayenne into the skillet with the sweet potato.
Cook for another minute, stirring constantly, until fragrant.
Transfer the sweet potato mixture to the bowl with the beans and kale.
Mix everything together with a fork until well combined.
Let the mixture rest for 5-10 minutes. If it seems too wet to hold its shape, stir in a little flour.
Taste and adjust seasoning as needed.
Shape the mixture into 4 to 6 evenly sized patties. Wipe out the skillet and return it to medium heat with the remaining 2 tablespoons (30 ml / 1 fl oz) of oil or butter.
Carefully place the burgers in the hot pan.
Cook for about 5 minutes per side, until nicely browned, firm, and cooked through.
Add more oil if the pan becomes too dry.
Serve immediately on buns with your favorite toppings or on a plate with a side salad.
Let the burger mixture rest for at least 10 minutes before shaping. This allows the breadcrumbs to absorb moisture and helps the patties bind together.
