Dissolve yeast in water with part of the sugar. Put flour in a bowl, make a well in the center, and carefully pour in the yeast mixture. Mix to combine. Cover and let the dough rest in a warm place for approx. 15 min.
Add margarine, remaining sugar and salt, and knead the dough until smooth. Set aside for approx. 30 min. more.
Knead the dough thoroughly once more, then roll it out on parchment paper into a rectangle. Transfer to a baking sheet and let it rest for another 15 min.
Preheat oven to 180°C/350°F. Cover the dough with plum jam. Then, sprinkle with sliced almonds (optional) and roll up from the long side, placing it seam side down on the baking sheet.
Brush with a beaten egg yolk. Bake in the oven at 180°C/350°F on the middle rack for approx. 40 min.
Set plum bread aside to cool, then serve.