In stand mixer or large bowl, rub sugar and saffron together with back of spoon until saffron turns to powder. Stir in 1/2 cup/125 mL boiling water and set aside until just warm. Sprinkle yeast over top. Let stand until frothy, about 10 minutes. Whisk in honey, eggs, yolks and oil.

In separate bowl, whisk together flour and salt; add to yeast mixture and stir until shaggy dough is formed. With dough hook attachment or by hand on floured surface, knead dough, dusting with a little extra flour if dough is sticking to bowl or surface, until smooth and elastic, about 10 minutes in mixer or 15 minutes by hand. Transfer to greased bowl, turning to grease all over. Cover with plastic wrap; let rise in warm, draft-free place until doubled in bulk, about 1-1/2 hours.

Lightly push down dough; transfer to work surface. Knead in raisins, pushing in any raisins that break the surface and kneading until dough covers them to prevent them from burning when baked. Cover with tea towel; let rest for 15 minutes.

Roll into 30-inch/75 cm long rope (once again, push in any raisins that break the surface). Holding one end in place, wind rope around that end to form fairly tight spiral, building it higher in the centre. Transfer to floured bread peel if using bread stone (preheat stone for 45 minutes), or to lightly greased or parchment paper-lined baking sheet. Let rise in warm, draft-free place until doubled in bulk, about 1 hour.

Glaze: Beat yolk with 1 tsp/5 mL water; brush over loaf. Sprinkle with sesame seeds.

Bake in centre of 350°F/180°C oven until golden brown and loaf sounds hollow when tapped on bottom, 35 to 45 minutes. (If top browns before bread is thoroughly cooked, cover loosely with sheet of foil for remaining baking time.) Let cool on rack.

Makes about 20 slices.

You can make the traditional 2 loaves of challah for Rosh Hashanah by dividing the dough into 2 pieces and rolling each into a 24-inch/60 cm long rope. Wind each rope into a spiral and bake side by side on baking sheet or bread stone for 25 to 35 minutes.