Prepare the yeast in a large mixing bowl for a stand mixer by whisking it with warm water and 1 teaspoon sugar (that helps activate the yeast). Let stand until it foams and puffs up, about 10 minutes. If it doesn’t get foamy, your yeast is either bad or the water was too warm or cool. Try again!
Using the whisk attachment for the stand mixer, or you can totally do this by hand, mix the remaining sugar, eggs, oil, and honey. (You can use a whisk if you’re doing this by hand.) Gradually add 3 cups flour and matcha green tea powder and then salt, either using a hook attachment with the stand mixer on medium speed or a spoon and your hands until the dough begins to pull away from the sides adding flour as needed. Dough should still be slightly sticky and soft. Add more flour if the dough is very sticky and knead for 10 minutes. You may not need all the flour.
Place the dough in a bowl greased with oil and cover. Let dough rise in a warm place until it has at least doubled in size, about 2–3 hours. I put mine on top of an oven heated to the lowest temperature.
Now time to braid! You can make two smaller challot or one large challah. I made one large one. Divide the dough into 6 equal size pieces. I used a food scale to be precise.
Take each piece and make six even strands. If you are having trouble getting them to roll out, let the gluten relax and try again. Line them up and pinch at the top to secure the end. Then take the strand on the right and move to all the way to the left. And the strand to the left and move it all the way to the right. Take the left strand, and place it in the middle between the strands, and replace it on the left with the second strand from the right. Then place the right strand in the middle and replace with the second strand from the left. Keep repeating until you reach the end. Secure the other ends together and tuck them under the challah.
Then let your challah proof again on a parchment lined baking sheet, lightly covered, until doubled in size and appears light and fluffy, about 45 minutes or so (exact proofing timing for challah will depend on environmental conditions.) Pre-heat the oven to 350 degrees F. Whisk the last egg yolk with 1/2 tablespoon water and generously brush over challah, sprinkle with sprinkles, and bake for 30-35 minutes at 350 degrees, rotating pans halfway through. If the challah start to brown too fast, cover with foil until done.
Cool slightly and eat! Best fresh or freezes well.