Place currants in a small bowl.
Heat rum or apple juice in the microwave or a small saucepan until steaming.
Pour rum or juice over currants to soften them, let sit about 2 hours.
Drain and set aside.
In a separate bowl, whisk warmed milk with ¼ cup flour and ½ Tbsp active dry yeast.
Let sit about 15 minutes until yeast activates and bubbles.
Add sugar, a beaten egg, lemon and orange zest, cinnamon, salt, cardamom, nutmeg, melted butter, vanilla extract and remaining flour.
Use a dough hook to mix the dough. Mix until the dough pulls away from the sides of the bowl cleanly and becomes slightly elastic. When touched with your finger it should stick but pull away cleanly. This should take 5 or 6 minutes. If dough is still sticky, add up to ¼ cup additional flour.
Continue kneading another 10 minutes until dough is smooth.
Remove dough from mixing bowl and shape into a ball.
Transfer dough to a lightly floured work surface.
Flatten dough into a large oval about 1/2 inch thick. Sprinkle the soaked and drained currants evenly over the surface.
Fold dough into thirds.
Turn and fold into thirds again to incorporate the currants.
Reshape dough into a round ball.
Transfer to lightly oiled mixing bowl. Cover and let rise until double in size, about 2 hours.
Once risen, transfer dough to a lightly floured work surface.
Divide dough into 16 equal pieces.
Line a baking sheet with a silicone mat or wax paper.
Roll dough pieces into round balls and place on the baking sheet. Arrange evenly
Let rise 15 minutes.
While balls rise, mix 1/4 cup water and 1/3 cup flour together in a mixing bowl until mixture is thick enough to hold its shape but thin enough to pipe with a piping bag.
Transfer mixture to a piping bag and carefully pipe crosses on top of each roll.
Let rise another 15 minutes until the dough is double in size from when it was first rolled into balls. Use this time to preheat oven to 425 degrees F.
Bake rolls for approximately 15 minutes until golden brown.
Remove from oven and let cool on the pan.
While rolls are cooling, combine 1/4 cup powdered sugar and 3 tablespoons warm water and whisk until sugar dissolves and mixture is lump free, add free squeezed juice and stir well.
Glaze rolls with this mixture while they are still warm/hot.
Enjoy the buns the same day.