In the bowl of the stand mixer, stir together the yeast, 2-¼ cups of flour, salt, sugar, cinnamon, and nutmeg. Add the mashed potato and butter and cream the mixture together using the paddle attachment.
Add the raisins, eggs, warm water, and milk. Continue mixing on low.
Add the rest of the flour ¼ cup at a time and mix well. Continue until the dough is easy to handle.
Using the dough hook, knead the dough until smooth. Or you can turn the dough out onto a lightly floured board and knead until smooth. Put the dough into a greased bowl and cover with a towel. Allow to rise until doubled, about 1-½ hours.
Preheat the oven to 375° F/190° C.
After dough is risen, punch it down and divide it into two equal pieces. Shape each piece into 16 round buns. Please buns on prepared baking sheets spaced 2 inches apart. Let rise until doubled, about 30 minutes.
Stir together the egg yolk and cold water to make a glaze. Brush the buns with the glaze, and bake in preheated oven for 20 to 25 minutes, until golden brown on top.
Remove buns from oven and put them on cooling racks. While buns are still warm, pipe a cross on top of each.
While the buns are baking, stir together the milk and confectioners sugar in a small bowl until you have a glaze with the consistency of frosting. It should not be runny, and you should be able to put it into a piping bag and squeeze it out.
Equipment:stand mixer with paddle and dough hook attachments large bowl, lightly coated with cooking spray 2 or 3 baking sheets, greased or lined with parchment paper (or 2 9×9 pans, greased) small bowlRecipe Notes:Prep time includes rising time.Use active dry yeast: Add 2 packages active dry yeast to ½ cup warm water and stir to dissolve. Add with the milk and eggs, and continue as above.Make ahead tip: Make the buns the night before. Warm them and pipe the icing just before serving.