Step 1

Place poppy seeds into a food processor and process until seeds are ground, about 1 minute.

Step 2

Mix poppy seeds with 3/4 cup sugar, 1 tablespoon melted butter, lemon juice, and hot milk in a bowl; stir to combine. Cover poppy seed filling and refrigerate while making bread (filling will set up and thicken as it chills).

Step 3

Mix yeast with water and 2 tablespoons sugar in a small bowl. Allow to stand until the yeast forms a creamy layer.

Step 4

Whisk flour with salt in a bowl; use a pastry cutter to cut 1/4 cup butter into the flour mixture until the mixture resembles coarse crumbs.

Step 5

Pour yeast mixture and egg yolk into flour mixture and stir to make a soft dough.

Step 6

Turn dough out onto a floured work surface and knead until smooth and slightly springy, about 5 minutes. If dough is too sticky, knead in more flour, about 2 tablespoons at a time.

Step 7

Cut dough into 2 equal pieces. Roll each piece out into a 12x16-inch rectangle.

Step 8

Spread half the poppy seed filling over each rectangle, leaving a 1-inch border. Fold the 1-inch border back over the filling on all sides and press down.

Step 9

Pick up the shorter side of a dough rectangle and roll it like a jelly roll; repeat with second rectangle. Pinch ends together or tuck ends under to prevent filling from leaking out.

Step 10

Line a baking sheet with parchment paper; place rolls seam sides down on the baking sheet and allow to rise in a warm place until doubled, about 1 hour.

Step 11

Preheat oven to 350 degrees F (175 degrees C).

Step 12

Beat egg white in a bowl until frothy; brush the rolls with beaten egg white.

Step 13

Bake in preheated oven until dark golden brown on top, 30 to 40 minutes. Remove from oven and cover rolls with a clean kitchen towel until cool to keep crust soft. Cool completely before slicing.