Cover the dough and allow it to rest, covered, for about 45 minutes. It won’t visibly rise very much. Line a rimmed baking sheet with unbleached parchment paper, and set it aside.

Divide the dough into 8 approximately equal pieces. Working with one piece at a time on a surface lightly dusted with tapioca starch, roll each piece of dough into a tight ball.

While the buns are nearly done rising, preheat your oven to 350°F and make the egg glaze. In a small bowl, place the egg and beat it well. Add the 1/4 cup of confectioner’s sugar, and beat to combine well. You should have a thick, shiny glaze.

Once the rolls have finished rising, with a sharp knife, slice a cross (+) on top of each roll about 1/4-inch deep. Using a pastry brush, brush the top of each bun generously with the egg glaze.

Place the baking sheet in the center of the preheated oven and bake until the buns are golden brown and firm to the touch, about 30 minutes. Allow the buns to cool for about 10 minutes on the baking sheet before transferring them to a wire rack to cool completely.

Once the buns are cool, make the icing for the cross. In a medium-sized bowl, combine the ½ cup confectioner’s sugar with 1 teaspoon milk. Mix to combine well. It will form a thick paste. Thin it with some more milk, a drop or two at a time, until it falls off the spoon slowly but steadily.

Once the rolls have cooled completely, place the icing in a pastry bag fitted with a small, plain tip, and pipe a cross (+) neatly over the cross you made with a knife, on each roll. If you attempt to ice the cross before the rolls are completely cool, the icing will melt and run.

Allow the icing to set and serve. Leftovers can be frozen in a single layer, then wrapped tightly with freezer-safe wrap. Defrost at room temperature, then sprinkle lightly with water and refresh in a warm toaster oven.