Add the saffron threads and 1 teaspoon of the measured sugar to a mortar and pestle. Grind until the saffron is broken down into a fine powder. Set aside.
In the bowl of a stand mixer, dissolve the yeast in the warm water. Let it sit for about 5 minutes, until foamy.
Stir in the lukewarm milk, sugar, softened butter, eggs, cardamom, saffron mixture, and salt.
Add 3 cups of flour and with the dough hook, mix until smooth. Gradually stir in 1 1/2 to 2 more cups of flour (we usually use 4 1/2 cups of flour total), just until the dough is soft and easy to handle.
Turn dough onto a lightly floured surface and knead until smooth and elastic (about 6 - 8 minutes).
Place in a greased bowl, cover, and let rise until doubled (about 1 hour).
Punch down dough. Divide into 24 pieces and shape each loosely into a short log. Cover and let rest for about 10 minutes before rolling into ropes. Roll each piece into an 8- to 10-inch rope and shape into an S. Curl both ends inward to form a loose coil and place buns onto greased baking sheets. Place one raisin in the center of each coil.
Brush tops lightly with softened butter. Let rise until noticeably puffy and close to doubled in size (about 30–45 minutes).
Bake at 350°F for 18 - 20 minutes, or just until lightly golden. Do not over-bake, or the buns can dry out quickly. Brush with butter after baking if you’d like the rolls to be even softer.
In a small bowl, mix powdered sugar with a little water or milk to create a thin glaze. Drizzle or spread over cooled buns.
Best fresh. These buns are softest the day they are baked. Warm leftovers briefly before serving.