Extra-Rich Sweet Yeast Dough:
2 1/4-ounce packages (4-1/2 teaspoons) active dry yeast, or 2 .6-ounce cakes fresh yeast
1/2 cup warm water (105°F to 115°F for dry yeast; 80°F to 85°F for fresh yeast), or 1/4 cup warm water and 1/4 cup warm milk, or 1/2 cup water mixed with 1/4 cup nonfat dry milk
1/2 cup sugar
1 cup unsalted butter or margarine, softened
4 large eggs
1-1/2 teaspoon salt
About 4-1/4 cups flour
1 large egg yolk, beaten slightly
1 teaspoon water
3 cups (about 1 pound) poppy seeds (ground)
1-1/2 cups water
1-1/2 cup sugar or honey; or 1 cup honey and 1/3 cup light corn syrup
2-1/2 tablespoons fresh lemon juice
1/2 teaspoon grated lemon juice
pinch of salt
Make Yeast Dough:
Dissolve the yeast in 1/4 cup of warm water (105°F to 110°F). Stir in one teaspoon sugar and let stand until foamy, 5 to 10 minutes.
Add the remaining water, sugar, butter (or margarine), eggs, and salt. Blend in 1-1/2 cups flour. Add enough of the remaining flour, 1/2 cup at a time, to make a workable dough.
On a lightly floured surface or in a mixer with a dough hook, knead the dough, adding more flour as needed to prevent sticking, until smooth and springy, about 5 minutes. Place in an oiled bowl, turning to coat. Cover and let rise in a warm, draft-free place until nearly double in bulk, 1-1/2 to 2 hours, or cover with plastic wrap and refrigerate overnight. (To test if the dough is sufficiently risen, press two fingers 1" deep into the center; if the indentation remain, the dough is ready) Also, you can refrigerate for at least 1 hour and up to 2 days.
Punch down the dough. Fold over and press together several times (this redistributes the yeast and its food). Let stand for 10 minutes.
Make Filling and Assembly:
Grind the poppyseeds or have them ground at the grocery store. Combine all the ingredients in a small saucepan and simmer over medium-low heat, stirring frequently, until the mixture thickens, about 12 minutes. It should be thick and may take longer. Let cool. Store in the refrigerator for up to one week.
Preheat oven to 350°F. Line several large baking sheets with parchment paper or grease them.
Divide the dough in half or thirds. On a lightly floured surface, roll out each piece into a very thin rectangle. (The thinner the dough, the thinner the cake layers.) Roll out each piece into a rectangle about 1/8" thick. Half will be about 15"x8" (thirds 10"x8"). Spread with the filling, leaving a 1/2" border along the edges. Starting from a long edge, roll up jelly roll style. Place on the prepared sheet. Baking without letting the cake rise produces thin alternating layers of pastry and filling. For slightly thicker cake layers, cover and let rise for about 40 minutes. Brush with egg wash.
Bake until lightly browned, about 35 minutes. Place the baking sheet on a wire rack to cool.