Warm 1 cup of Whole Milk until lukewarm (about 105–110°F / 40–43°C), stir in 1 tablespoon of Granulated Sugar and 2 teaspoons of Instant Yeast, then let sit 5–10 minutes until foamy.
In a large bowl combine 4 cups of All-Purpose Flour with 1 1/2 teaspoons of Salt and the zest of 1 Lemon Zest. Make a well, add 3 Egg Yolks, 1 teaspoon of Vanilla Extract and the activated yeast mixture; stir to form a shaggy dough.
Knead the dough on a lightly floured surface until it starts to come together, then gradually work in 6 tablespoons of softened Unsalted Butter until the dough is smooth, elastic and slightly tacky. Place in a greased bowl, cover, and let rise until doubled, about 1–1 1/2 hours.
While the dough rises, prepare the filling: gently heat 1 cup of Whole Milk with 1/3 cup of Honey and 1/3 cup of Granulated Sugar in a saucepan, just to scald; remove from heat and stir in 2 cups of ground Poppy Seeds (or grind whole seeds very fine). Let sit to absorb liquid and cool slightly.
Fold into the poppy base 1/4 cup of softened Unsalted Butter, 1/2 cup of chopped Walnuts, 1/2 cup of Raisins (soaked if desired), and 1/3 cup chopped Candied Orange Peel. Add 1 teaspoon Vanilla Extract and the zest of 1 Orange Zest for brightness. If mixture seems too wet, stir in 1/4–1/2 cup of Fine Dry Breadcrumbs to thicken.
In a separate bowl, whisk 3 Egg Whites to soft peaks and gently fold into the poppy mixture to lighten it. Taste and adjust sweetness or texture with additional Granulated Sugar or Fine Dry Breadcrumbs as needed.
Punch down the risen dough and roll it on a lightly floured surface into a rectangle about 12x18 inches. Lightly brush the surface with melted Unsalted Butter and sprinkle a thin layer of Fine Dry Breadcrumbs to keep the filling from making the dough soggy.
Spread the poppy filling evenly over the dough, leaving a 1-inch border. Roll up tightly from the long side into a log, pinch seams and ends to seal, and place seam-side down on a parchment-lined baking sheet. Tuck the log into a gentle curve if desired.
Cover the roll and let rise until puffy, about 30–45 minutes. Preheat the oven to 350°F (180°C). Brush the top lightly with a beaten egg or melted butter, then bake 35–45 minutes until deep golden and cooked through (cover loosely with foil if browning too quickly).
Cool the roll on a wire rack. For the finishing glaze, whisk together 1 cup of Powdered Sugar with 1 tablespoon of Lemon Juice and 1–2 teaspoons of Hot Water until smooth and pourable. Drizzle over the cooled roll, slice, and serve.
