Dissolve the yeast in the lukewarm water. Add 1 up (4 oz/125g) of the flour and 1 tablespoon sugar and let stand for 1 hour.
Place the remaining flour in a large bowl. Make a well in the center and place the remaining sugar, butter, salt, eggs, egg yolks, aniseed and the yeast mixture in the well. Mix thoroughly, then knead on a floured board until the dough becomes elastic and bubbles form.
Place the dough in a greased bowl, cover with a cloth and let rise in a warm, draft-free place until doubled in volume.
Punch down the dough, form into 2 round loaves and place on a greased baking pan. Let the dough rise in a warm place until doubled in volume again.
Preheat the oven to 375 degrees (190 C). Make several slashes across the top of the loaves, brush with the egg wash and, if desired, sprinkle with sesame seeds. Bake for 35-40 minutes.