Combine the water and yeast. Let stand for about 5 minutes. Add 90g flour, 33ml sugar, and salt; mix until well combined. Add egg yolks and remaining flour. Mix until combined, then knead dough in bowl until all flour is incorporated.
Turn onto a floured work surface; knead a few minutes until smooth. Knead in Flora Gold margarine until incorporated.
Place the dough into a well-oiled bowl, turning several times to coat entirely with oil. Cover tightly with plastic wrap, and refrigerate overnight.
Bring dough to room temperature, about 30 minutes. On a lightly floured work surface, roll out dough into a 28 cm square, about 1cm thick. Cut out about 40 5cm rounds. Re-rolling when necessary.
Lightly beat egg whites. Brush edge of a dough round with egg white, then mound ¼ teaspoon jam in center. Top with another round; press edges to seal. Repeat with remaining rounds. Allow to rise until puffy, 20 to 30 minutes.
Deep fry at 160°C working in batches of 4 or 5, slip doughnuts into hot oil. Fry, turning once, until golden brown, about 1- 3 minutes. Using a slotted spoon, transfer doughnuts to paper towels to drain.
While doughnuts are still hot, dip them in remaining ¼ cup sugar, turning to coat. Serve immediately.