Old World Poppy Seed Roll

Poppy Seed Filling:

• ½ pound poppy seeds
• ¾ cup white sugar
• ½ cup hot milk
• 1 tablespoon butter, melted
• 1 teaspoon lemon juice

Bread:

• ½ cup warm water (100 degrees F/38 degrees C)
• 2 tablespoons white sugar
• 1 (.25 ounce) package active dry yeast
• 2 cups all-purpose flour, or more if needed
• ½ teaspoon salt
• ¼ cup butter
• 1 large egg, separated - white reserved