In a small saucepan, combine the milk, 1 tablespoon of sugar, and the saffron threads. Heat over medium-low heat, stirring to dissolve the sugar. Once the milk is steaming, remove from the heat and let cool to 110˚F (43˚C).
Sprinkle the yeast over the milk and let bubble, about 5 minutes.
In a large bowl, whisk together the flour, remaining sugar, salt, and cardamom.
Make a well in the center of the flour and pour in the milk, 2 eggs, sour cream, and butter. Stir to combine, then, once the dough starts to come together, use your hands to incorporate fully.
Turn the dough out onto a clean surface and knead until the dough is springy, about 5 minutes.
Place the dough in a large bowl and cover with plastic wrap. Let rise in a warm place for 1 hour, or until doubled in size.
Punch down the dough and flip onto a clean surface.
Divide the dough into 12 equal pieces. Form each piece into a ball about 2 inches (5 cm) wide, then roll into a cylinder about 12-14 inches (30 cm) long
Swirl the dough into a S shape starting at one end until the middle and then the other end.
Transfer the dough to a parchment paper-lined baking sheet, cover with plastic wrap, and let rise for 30 minutes, until doubled in size.
Preheat the oven to 400°F (200°C).
Beat the remaining egg and brush over the dough swirls. Place a single raisin or chocolate chip in the center of the swirls on each end.
Bake the buns for 10-12 minutes, or until golden brown and cooked through.