Rice the hot boiled potatoes directly onto a clean work surface or into a large bowl. Spread them out and let steam escape for 5 minutes until no longer wet-looking.

Add the egg yolk and salt to the riced potatoes and mix briefly with a fork.

Add the flour (and semolina if using) and bring everything together with your hands until a smooth, soft dough forms. Do not overwork. If the dough sticks to your hands, add flour 1 tbsp at a time.

Wrap the dough in cling film and refrigerate for 20 minutes.

Bring a large wide pot of salted water to a gentle simmer.

Lightly flour your hands and the work surface. Divide the dough into 16 equal pieces, roughly 50 g each.

Flatten each piece into a round disc about 8 cm across. Place one plum in the center.

Fold the dough up around the plum and pinch the seam firmly closed, rolling the dumpling gently between your palms to form a smooth ball. No gaps.

Lower the dumplings into the simmering water in batches of 6 to 8. Do not crowd the pot.

Cook for 12 to 14 minutes total, until the dumplings float and then continue cooking for 3 to 4 minutes after surfacing.

Remove with a slotted spoon and drain briefly on a clean cloth.

Melt the butter in a frying pan over medium heat. Add the breadcrumbs and stir constantly for 3 to 5 minutes until deep golden brown and fragrant.

Remove from heat immediately so they don't burn.

Place 4 dumplings per person in a deep bowl or plate. Spoon the toasted breadcrumbs generously over the top.

Dust with powdered sugar and serve with a dollop of quark or tvaroh on the side.