Scalding the milk: Heat milk in a small saucepan until steaming or 180F. Remove from heat and let cool to just barely lukewarm or room temperature.
Plump the raisins (if using): Place raisins in a small bowl. Cover with very hot or boiling water and let stand 15 minutes. Drain and dry well before adding to dough.
Dissolve yeast in lukewarm water (about 110F) and the 2 tsp. sugar. Let stand for 10 minutes.
In a large bowl or the bowl of a stand mixer with a kneading hook, combine the scalded milk, butter, 1/2 cup sugar, salt, vanilla and lightly beaten eggs. Beat in the yeast mixture. Beat in the flour 1 cup at a time, adding the spices with the third cup of flour, and desired raisins/peel/currants with the fourth cup of flour, making sure the fruit is well covered with flour before mixing in.
Start kneading with hands or mixer, adding only enough of the last cup of flour to keep dough from sticking. Knead at least 5 minutes. Place dough into a greased bowl, sprinkle lightly with flour, cover with a damp cloth and leave in a warm, draft-free place until doubled in bulk.
Punch down dough. Cover again with flour and damp cloth and leave to rise another 30 minutes.
Preheat oven to 350F.
Divide dough into equal-sized pieces and form into balls as follow:16 buns - to be baked in two loaf pans (9x5-inch works best) with 8 rolls in each
20 buns - to be baked in a 9x13 baking pan in 5 rows of 4
*I like to weigh the dough and divide that number by the number of buns I want to make, then weigh out each piece to that weight. That way all the buns will be exactly the same size.
Place into greased baking pan(s).
Set buns out to rise until doubled in bulk.
Bake in a preheated 350° F. oven for 35-40 minutes or until golden brown and hollow sounding when tapped (or at least 190F when tested with an instant read thermometer). *Check them at 30 minutes and cover loosely with aluminum foil for the last part of baking, if already browned enough. They can seem "done" at about 30 minutes, but are probably not. Baking time should be at least 35-40 minutes).
Meanwhile, prepare the sugar glaze by stirring together the sugar and hot water.
Remove from oven and immediately brush tops of buns with the sugar glaze.
Allow buns to cool for 8-10 minutes in pan, then remove (in one large piece) to a cooling rack to cool completely. (Do not separate buns until ready to eat, to keep them nice and soft inside).
Once cooled or before serving, prepare the icing by beating together all the icing ingredients. Start with 2 tsp cream or milk and add more, a tiny bit at a time, until icing is piping consistency. Use a pastry bag or a ziploc bag with the corner snipped off to pipe a cross of icing on top of each bun.