In mortar with pestle or in bowl with back of spoon, crush saffron with sugar until powdery; mix with 1/4 cup/60 mL warm water until sugar is dissolved. Sprinkle yeast over saffron mixture; let stand until foaming, 5 to 10 minutes.

In large bowl, whisk together buttermilk, honey, salt, egg and yolks. Stir in yeast mixture and about one-third of the all-purpose flour; beat well with wooden spoon until batter is smooth and sticky. Beat in softened butter until smooth. Stir in spelt flour and all but about 1/4 cup/60 mL of the remaining all-purpose flour until soft dough forms.

Sprinkle some of the remaining flour on work surface and knead, adding additional flour if necessary, until dough is moist but silky smooth, 5 to 10 minutes. Place in buttered bowl; cover and let rise in warm place until doubled in bulk, about 1-1/2 hours.

Butter two 9-inch/2.5 L metal cake pans. Lightly punch down dough; knead lightly. Divide dough in half; form into 2 balls and let rest for 10 to 15 minutes.

Roll 1 ball into rope and cut into 10 equal pieces; form each piece into ball, pulling down sides of dough and pinching to seal on bottom. Arrange evenly spaced in one of the prepared pans. Repeat with remaining dough. Brush tops with melted butter. Cover and let rise in warm place until doubled in bulk, 30 to 45 minutes.

Bake in centre of 375F/190C convection or 400F/200C conventional oven until golden brown and centremost rolls are cooked through, about 17 minutes (to test, insert knife into centre for 5 seconds and touch to finger; if knife is hot, rolls are done). Serve warm.

Makes 20 buns.