Place the currants or raisins in a bowl and cover with 1 cup of boiling water. Let soak for 10 minutes, then drain well, and set aside.
In the bowl of a stand mixer, stir together the milk, ½ teaspoon sugar, and the yeast. Let the mixture sit until it’s very foamy on top, about 10 minutes.
To the yeast mixture, add the remaining ½ cup of sugar, 1 egg, and the melted butter. Then, add the flour, salt, cinnamon, allspice, and nutmeg. Attach the dough hook and mix on low speed to start combining. Once the ingredients are mostly incorporated, increase the speed to medium-low and continue mixing until a tacky and elastic dough has formed and is making a “slapping” sound against the sides of the bowl, about 6 minutes. (The dough may still cling to the very bottom of the bowl and should feel tacky but not stick to you when you touch it.)
Mix in the drained raisins and knead for 30 more seconds. Transfer the dough to a lightly oiled bowl, and turn to coat the dough in oil. Cover and let rise until doubled in size, about 1½ hours.
Lightly grease a 9x13-inch baking pan with baking spray or butter.
Transfer the dough to a lightly floured surface and divide it into 12 equal pieces. To shape each piece into a ball, gather the edges into the center and pinch them together. Flip the ball over, cup your hand around it, and move your hand in a circular motion. This will create tight smooth dough balls.
Place the dough balls in the prepared pan spacing them equally apart. Cover and let rise again until they are almost doubled in size, about 1 hour.
After 45 minutes of rise time, preheat the oven to 375°F.
When the buns have risen, beat the remaining egg with 1 teaspoon of water or milk and brush the tops lightly with egg wash.
For the Cross Topping:
In a small bowl, stir together the flour and water until a thick paste forms. Transfer it to a piping bag or a ziptop bag with one corner cut off.
Pipe a straight line through the center of each bun. Repeat making the second set of lines perpendicular to the first set, forming a cross on top of each bun.
Bake for 20 minutes or until golden brown on top. Let cool in the pan for 10 minutes.
For the Glaze:
In a small bowl, whisk together the powdered sugar and water until smooth. Brush the glaze over the warm rolls before serving.
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Notes
Use unexpired yeast. If your yeast has expired, the buns may not rise well. Always check the expiration date before starting a yeasted bread recipe. If the yeast doesn't get very foamy after 15 minutes in the warm milk, start over with a new yeast packet.
Measure the flour correctly. Using too much flour will cause the buns to turn out dry and dense. To avoid this, weigh the flour with a kitchen scale for the most accurate measurement. If you don't have one, fluff the flour, spoon it into your measuring cup, and level off the top with a knife.
For additional flavor, add grated orange zest (the zest of 1 orange peel) to the dough when adding the drained currants. You can also include other spices like ½ teaspoon of ground cardamom or cloves.
Choose a good rising spot. Avoid drafty, cold areas and aim for a warm place so the dough can rise properly.