For dough: In a small bowl, whisk together warm milk, 1 tablespoon (12 grams) granulated sugar, and yeast. Let stand until foamy, about 5 minutes.

In the bowl of a stand mixer, stir together all-purpose flour, salt, and remaining ½ cup (100 grams) granulated sugar by hand until combined. Add yeast mixture, melted butter, and egg yolks; using the paddle attachment, beat at low speed until combined. Switch to the dough hook attachment, and beat at medium-low speed until a smooth, elastic, and slightly tacky dough forms, 6 to 8 minutes.

Lightly spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 1 to 1½ hours.

Preheat oven to 325°F (170°C). Line a rimmed baking sheet with parchment paper.

For filling: In a medium bowl, whisk together poppy seeds and almond flour.

In a medium saucepan, heat granulated sugar, milk, and orange zest over medium heat, stirring occasionally, until sugar dissolves and mixture just begins to simmer. (Do not boil.) Remove from heat; stir in poppy seed mixture until combined. (Mixture may appear dry or sandy.) Let cool completely. (See Note.)

In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites at medium-high speed until stiff peaks form, 3 to 5 minutes. Fold egg whites into poppy seed mixture until combined.

Punch down dough. Very lightly dust work surface with all-purpose flour; turn out dough onto prepared surface, and divide in half. Roll half of dough into a 12x9-inch rectangle, with one long side closest to you. Spread half of filling (about 1 cup or 285 grams) onto dough, leaving a ¼-inch border on both short sides and one long side. Starting with long side opposite border, roll up dough into a log, pinching and tucking ends to seal. Place log, seam side down, on parchment paper, and loosely wrap parchment around dough, leaving about ¼ inch of space around top and sides of log. Place on prepared pan. Repeat with remaining dough and remaining filling.

Bake for 30 minutes. Discard parchment from around logs, and bake until golden brown and an instant-read thermometer inserted in center registers at least 190°F (88°C), 15 to 20 minutes more. Let cool on pan for 10 minutes. Remove from pan, and let cool completely on a wire rack.

For glaze: In another medium bowl, whisk together confectioners’ sugar and 1½ tablespoons (22.5 grams) water. Pour onto loaves. Garnish with poppy seeds, if desired. Let stand until glaze is set, about 15 minutes. Refrigerate in an airtight container for up to 3 days.