Combine all the dry ingredients in a bowl, including flour, sugar, lemon zest, salt, and instant yeast. (If using European-style fresh yeast, use about 1 1/2 ounces fresh yeast and mix it with the wet ingredients instead of the dry.)

Warm the milk to just lukewarm, around 90 to 100 degrees.  Add in the butter to soften/melt.  Stir to combine.

Add the milk/butter in with the dry ingredients, and also add the egg yolk.  Stir to combine, and when it becomes too thick, start kneading.

Knead until a dough comes together and forms a smooth ball, around 1 to 2 minutes.

Cover with a cloth and set aside to rise for about 1 hour.

To make the filling, start by bringing the milk to a boil, then remove from heat and add the butter to melt.  Set aside to cool slightly.

Grind the poppy seeds until they're very fine. A hand crank mill or high powered blender (vitamix) work best, and will grind in just a few minutes. If using a standard food processor, it takes much longer and won't grind as fine. 

Once the poppyseeds are about ground, toss the almonds and raisins in to grind as well, until it's all a uniform fine groundmass.  (If you're using plum butter instead of raisins, just mix that in with the wet ingredients.)

Pour in the slightly cooled, boiled milk.  Stir to combine.

Add the sugar and breadcrumbs.  At this point, it's cool enough that the egg won't cook. 

Add in the beaten egg, cinnamon, and almond extract.

Stir, and set aside. 

The breadcrumbs will absorb more milk as it sits, and the mixture will slowly thicken as it cools.

To assemble the mohnstrudel, divide the dough in half.  Flour a work surface and roll out one piece of dough it's a 14 x 18 inch rectangle (35 x 43 cm).

Spread the cooled filling all over the dough, making an even thick layer, but leaving about 1 1/2 inches (4 cm) as a border with no filling on all sides.

Starting on the long side, gently roll the dough into a log.  Tuck the ends under on both sides.

Repeat with the 2nd piece of dough.

Transfer to a prepared baking sheet, seam side down, and cover with a cloth to raise for about 20 to 30 minutes. 

While the roll rises again, preheat the oven to 350 F (180 C).

Brush the roll with melted butter, and then place it into the oven to bake for about 40 to 50 minutes.  Rotate the pan about halfway through the baking to encourage it to cook evenly. 

If the loaves are browning too much early in cooking, tent with aluminum foil.

When done, the loaf should be golden brown and sound hollow when tapped.

Allow it to cool fully on a rack before slicing.