Combine the flour, instant yeast, sugar, and salt in the bowl of a stand mixer. Stir briefly to distribute the yeast.

Add the warm milk and eggs to the dry ingredients. Mix on low with the dough hook until a shaggy dough forms, about 2 minutes.

Increase speed to medium and add the softened butter one or two cubes at a time, waiting for each piece to fully incorporate before adding the next. This takes about 8 minutes.

Continue kneading on medium-high until the dough is smooth, slightly tacky, and pulls cleanly from the sides of the bowl, about 5 more minutes.

Shape the dough into a ball, place in a lightly oiled bowl, cover with plastic wrap, and let rise at room temperature until doubled, about 60 to 75 minutes.

Grind the poppy seeds in a spice grinder in batches until they resemble a coarse grey powder. Don't over-grind to a paste.

Combine the ground poppy seeds, milk, sugar, butter, orange zest, lemon zest, honey, and vanilla in a small saucepan over medium heat.

Stir constantly and cook until the mixture thickens and pulls away from the sides of the pan, about 5 to 7 minutes. It should hold a slow-moving trail when you drag a spoon through it.

Transfer to a bowl and let cool completely to room temperature before using. Don't rush this step.

Punch down the risen dough and turn it onto a lightly floured surface. Roll into a rectangle roughly 45 cm x 35 cm and about 5 mm thick.

Spread the cooled poppy seed filling evenly across the dough, leaving a 2 cm border along one long edge.

Starting from the filled long edge, roll the dough tightly into a log. Pinch the seam closed along the border edge.

Transfer the log to a board, cover loosely, and refrigerate for 15 minutes to firm up.

Slice the log into 12 equal rolls using a sharp serrated knife. Each roll should be about 3.5 cm thick.

Arrange the rolls cut-side up in a greased 9x13-inch baking dish, leaving small gaps between each roll. Cover and let proof until puffed and touching each other, about 45 to 60 minutes.

Heat the oven to 180 C / 355 F with the rack in the center.

Bake the rolls for 25 to 30 minutes until the tops are golden brown and the dough sounds hollow when tapped. An instant-read thermometer inserted into the dough should read 90 C / 194 F.

While the rolls bake, whisk together the sifted powdered sugar, orange juice, lemon juice, and optional zest until smooth and pourable. The glaze should run off the spoon in a thin stream.

Remove the rolls from the oven and pour the glaze over them immediately. Let it soak in for 5 minutes before serving.