ln a small bowl, place yeast, 1 teaspoon sugar, and lukewarm water. Allow to sit around 10 minutes, until it becomes foamy on top.

In a large bowl or stand mixer fitted with the whisk attachment, mix together 1½ cups flour, salt, cardamom and sugar. After the water-yeast mixture has become foamy, add to flour mixture along with oil. Mix thoroughly.

Add another cup of flour and eggs until smooth. Switch to the dough hook attachment if you are using a stand mixer.

Add another cup flour and then remove from bowl and place on a floured surface. Knead remaining flour into dough, continuing to knead for around 10 minutes (or however long your hands will last).

Place dough in a greased bowl and cover with a damp towel. Allow to rise 3-4 hours.

Preheat oven to 350°F.

In a small bowl, whisk together tahini, silan, and pinch of salt. 

After the challah is done rising, roll out dough into a large rectangle, about ½-1-inch thick, on a lightly floured surface. The challah dough may need an extra dusting of flour to work with at this point.

Using an offset spatula or the back of a spoon, spread an even layer of the tahini-silan mixture all over the rolled-out dough. 

Working quickly, start rolling up the dough to-ward you. Try and keep the roll relatively tight as you go. Pinch the end and tuck under when you finish.

Create a pinwheel shaped-challah by snaking the dough around and around in a circle around itself. When finished, tuck the end under the challah neatly and pinch lightly. This doesn't have to be perfect.

Place round challah on a baking sheet lined with a silpat or parchment paper and allow to rise another 30-60 minutes. You can also place challah in a round pan.

Beat egg yolks with 1 teaspoon water. Brush liberally over challah. Combine salt, sugar, and cardamom in a small bowl and sprinkle evenly over challah.

Bake for 26-27 minutes, or until middle looks like it has just set and the color is golden.