Soak raisins.currants in hot water for 10 minutes.
Whisk milk, yeast and tsp sugar together, let stand 10 minutes.
Mix brown sugar, butter, eggs, vanilla, spices and 1 c ( 125 g ) flour 1 minute.
Add remaining flour ( 313g ) and raisins, Beat on low for about 5 minutes.
Grease or oil bowl and roll dough ball to coat.
Let rise in warm area ( bread proofing oven ) for about 3 hours.
Grease 9x13 baking pan, divide dough into 15 pieces ( about 65 g ).
Shape into ball and place in pan.
Cover with wrap and place in refrigerator overnite.
Remove form fridge and place in warming area to rise another 2-3 hours.
Preheat oven to 350
When fully risen, brush on egg wash - bake 15-20 mins ( internal temp 195 ).
Brush baked buns with most of glaze.
Strain remaining glaze to remove zest shards.
Add more powdered sugar to form icing.
Place in plastic bag and cut off tip to form piping bag.
Pipe a line down center of each row and repeat in other direction.