Grind the saffron with the 1 teaspoon of sugar to a fine powder in a mortar and pestle. Transfer to a small bowl, stir in the rum, cover, and let it steep for at least 30 minutes, or overnight at room temperature.
Soak the raisins in warm water while the saffron steeps, then drain and pat dry.
In a stand mixer, add the saffron mixture, cold milk and egg, rinsing the saffron bowl with a little of the milk. Add the flour, yeast, sugar and salt, and mix until a shaggy dough forms.
Knead until very smooth and the dough passes the windowpane test. It will be very sticky at first but comes together into one ball as you knead. Then add the butter a few pieces at a time and knead until fully worked in.
Cover and let rise until doubled in size, which may take an hour or longer depending on how warm your dough and kitchen are.
Punch the dough down and divide it into about 30 pieces. Roll each into a 6 to 8 inch rope and curl both ends in opposite directions into a reversed S. Place on parchment-lined baking sheets.
Cover and let rise until the dough springs back only halfway when poked, usually about 45 to 60 minutes. Heat the oven to 435°F (225°C), not convection.
Brush gently with the egg and milk, then press one raisin deep into the center of each curl, all the way down to the tray.
Bake one tray at a time on the middle rack until just golden with lightly browned bottoms, about 7 to 9 minutes.
Cool under a clean kitchen towel. Serve warm.
