Peel and cut the Russet Potatoes into chunks and boil in unsalted water until very tender; drain and mash or rice them while still hot until smooth. Let the mashed potatoes cool slightly.
Stir a beaten Egg into the cooled mashed potatoes, then gradually add Wheat Flour and a pinch of Salt until you have a soft, slightly sticky dough that holds together—be careful not to overwork it.
While the dough rests, finely dice the Salted Pork and chop the Yellow Onion. In a skillet, render the pork over medium heat until it starts to crisp, then add the onion and cook until translucent and golden.
Season the pork and onion filling with a generous pinch of freshly ground Black Pepper and a light dusting of Allspice; taste and adjust seasoning. Remove from heat and let the filling cool enough to handle.
Portion the potato dough into even pieces. Flatten each piece in your palm into a disc, spoon a small amount of the pork-onion filling into the center, then carefully fold and seal to form a smooth dumpling.
Bring a large pot of Water to a gentle boil with a little salt added. Reduce to a simmer and gently lower the kroppkakor in batches; cook for about 10–15 minutes, until they float and feel firm all the way through. Avoid overcrowding the pot.
Lift the cooked dumplings with a slotted spoon and drain briefly on a rack or paper towel. In a separate pan, melt Butter and, if you like, briefly brown the dumplings a moment on each side for a bit of color and extra flavor.
Serve the kroppkakor warm, spooning extra melted Butter over them and offering Lingonberry Jam on the side for the traditional sweet-tart accompaniment.
