large unpeeled Yukon Gold
, about 750 g
1 2/3 cups
, or spread
Cover potatoes with water in a large pot. Bring to a boil and reduce heat to medium. gently boil, partially covered, until soft, about 30 min. Drain and rinse with cold running water. Peel potatoes, then cut into large chunks. Use a ricer to mash until very fine. set aside on a baking sheet to cool slightly. stir 1 tbsp butter, salt and egg into potatoes until smooth. Refrigerate until completely cool, about 1 hour. stir in 1 cup flour just until combined. turn dough out onto counter. knead dough, adding 1/2 cup flour, until smooth. Let stand, covered with plastic wrap, for 30 min.
Melt remaining butter in a large frying pan over medium. add bread crumbs and stir often until slightly brown, about 4 min. Remove from heat, then stir in sugar and cinnamon. set aside to cool. Fill potato pot three-quarters full of water and bring to a boil.
Sprinkle the counter with remaining flour. Roll out dough into a 12 × 12-in. square about 1/2 in. thick. Cut dough into 16 3 × 3-in. squares. Put 1 tsp plum jam in centre of a square of dough. Pull the corners together to make a dumpling, making sure not to leave any gaps. Pinch edges to seal. Repeat with remaining dough and jam.
Slip dumplings, 1 at a time, into the boiling water. Do not crowd the pot. Using a slotted spoon, move dumplings around to prevent sticking. When the dumplings rise to the surface, let them cook 4 to 5 more min. Remove with a slotted spoon and dab on paper towels to remove excess water.
Drop hot dumplings into the crumbsugar mixture. Carefully roll them around until they are well coated. Dust with icing sugar and serve immediately.