In a saucepan, heat the milk, butter, and sugar until the butter is melted. Let it cool to about 100°F (40°C).

In a large bowl, beat the egg yolks with the yeast (dissolve fresh yeast in warm milk if using). Add the cooled milk mixture and sift in the flour with a pinch of salt.

Knead the dough for about 5 minutes until smooth and elastic. Cover the bowl with a cloth and let the dough rise in a warm place for about 1.5 hours, or until it has tripled in volume.

If making homemade poppy seed filling, follow the recipe instructions for preparation. If using store-bought filling, check the consistency and cook if necessary to remove excess moisture. Once cooled, gently fold in the beaten egg whites.

Transfer the risen dough to a lightly floured surface. Roll it out into a rectangle about 1/2 inch thick.

Spread the poppy seed filling evenly over the dough, leaving a small border around the edges.

Roll the dough tightly from one long edge to the other, forming a log. Place the roll seam-side down on a piece of parchment paper. Wrap the roll in the paper, leaving some space for expansion.

Preheat the oven to 350°F (180°C) for convection or 375°F (190°C) for conventional baking.

Place the wrapped roll on a baking sheet and bake for about 40 minutes.

After baking, open the oven door slightly and let the makowiec cool inside for 15 minutes. Transfer to a wire rack to cool completely.

Prepare the glaze by mixing powdered sugar with a small amount of water or lemon juice until smooth. Drizzle over the cooled makowiec and sprinkle with additional dry poppy seeds if desired. Allow the glaze to set before serving.