Mix the water, egg yolks, yeast, sugar, salt, and melted butter in a 6-quart bowl or a lidded (not airtight) food container.
Mix in the flour without kneading, using a heavy-duty stand mixer (with paddle), a danish dough whisk, or a spoon. The mixture will be quite loose because of all the yolks.
Cover (not airtight) and allow to rest at room temperature until the dough rises for 2 hours.
The dough will be loose, but will firm up when chilled. Don't try to use it without chilling for at least 3 hours. Refrigerate the container and use over the next 5 days.
To bake: Generously grease a parchment lined 8 ½ x 4 ½ -inch nonstick loaf pan. Dust the surface of the refrigerated dough with flour and cut off a 1-pound (grapefruit-size) piece. Dust the piece with more flour and quickly shape it into a round ball by stretching the surface of the dough around to the bottom, rotating the ball a quarter-turn as you go.
Roll the dough out to a ⅛-inch thick rectangle, about 12 x 15 inches. As you roll out the dough, add flour as needed to prevent sticking. (I like to roll out the dough on a silicone mat.)
Spread the lemon curd evenly over the dough. Sprinkle three-quarters of the streusel over the curd. Save some for the top.
Starting with the long side of the dough, roll it up into a log. Pinch the seam closed. Stretch the log until it is about 2 inches thick. Cut the log in half, lengthwise. Twist the 2 long pieces together, with the cut side facing up. Form an oval with the ends together and place in the prepared pan.
Cover loosely with plastic wrap and allow to rest at room temperature for 90 minutes.
Preheat the oven to 350 degrees F, with a rack placed in the center of the oven.
Sprinkle the loaf with the remaining streusel.
Bake the loaf for about 45 minutes, or until golden brown and well set.
Allow to cool on a rack completely before eating.
!Streusel topping
Combine all the streusel ingredients in a bowl and mix until the butter is roughly incorporated. Don't overmix--you want a crumbly texture. Set aside.
!Lemon Curd
Whisk together the yolks, sugar, lemon juice, and lemon zest in a large metal bowl.
Place the bowl over a pot of gently simmering water set up as a double boiler.
Stir constantly with a rubber spatula until the lemon curd begins to thicken, about 10 minutes.
Add the butter and continue to stir until it is completely melted and the curd thickens; it will be the consistency of smooth pudding.
If there are any lumps, strain the curd into a container; then cover with plastic wrap.
Set the container in the freezer until cool, and then refrigerate.