In the bowl of a stand mixer fitted with a paddle, mix together yeast, milk, saffron, and 1 teaspoon sugar; let sit until foamy, about 10 minutes.
Stir in the remaining sugar, along with the flour, salt and 2 of the eggs. Mix on low speed until dough forms and gathers around the paddle. Replace paddle with dough hook and add butter; knead on medium-high speed until dough pulls away froms ides of bowl, 8 minutes. Transfer dough to a large bowl greased with oil and cover with plastic wrap; let rest in a warm place until doubled in size, 1 hour.
Divide dough into 32 pieces and roll each piece into an 8-inch long rope. Form each rope into an S-shape and then roll each end into a tight sprial (maintaining S-shape). Place shaped dough pieces 2 inches apart on parchment-lined baking sheets; cover with plastic wrap and let rise in a warm place for 30 minutes.
Heat oven to 400°F Uncover the dough pieces and place a raisin at the center of each of the spirals. Lightly beat remaining egg with 1 tablespoon water and brush each bun with egg mixture. Bake until buns are golden brown and cooked through, 16 minutes. Transfer buns to a wire rack and let cool for at least 10 minutes before serving.