Kroppkakor - Swedish potato dumplings

1) Boil potatoes in a saucepan of salted water until tender, about 20 minutes.
2) Drain potatoes then transfer to a bowl and mash until smooth.
3) Add flour, eggs, yolk, and salt; stir to combine. Cover with clingfilm and chill dough 30 minutes.
4) Heat oil and bacon in a frying pan over medium-high heat; cook until fat is just rendered, 10–12 minutes.
5) Add onion and cook, stirring occasionally, until onion is golden and bacon is crisp, about 8 minutes.
6) Pour off the fat and stir allspice and salt into bacon mixture; let cool.
7) Bring a large saucepan of salted water to a boil.
8) On a lightly floured surface, divide dough into fourteen balls.
9) Take one ball and with lightly floured hands, press index finger into center of ball to create a pocket; place about 2 tbsp. bacon mixture inside pocket and pinch edges of dough to seal; roll into a smooth ball and flatten into a 5cm wide patty about 2.5cm thick. Repeat with remaining balls.
10) Add dumplings to water; when dumplings float, reduce the heat to medium and simmer until firm, about 30 minutes.
11) Using a slotted spoon, transfer the dumplings to a serving platter; serve with loganberries and sour cream.