Place the flour into a large bowl. Crumble the fresh yeast into the flour and mix well; if using active dry yeast, whisk the yeast into the 2 cups of water in a separate bowl and add the yeast and water mixture into the flour. Place the sugar, whole egg, 1 egg yolk and the sunflower oil into the flour. Mix the ingredients by hand or with a stand mixer fitted with a dough hook until they just come together to form a dough. Add the salt and knead the dough until it is smooth and uniform, about 8 more minutes. 

Grease the surface of a clean and large bowl with 1 teaspoon of sunflower oil. Form the dough into a ball and place it into the bowl. Lightly cover the bowl with plastic wrap and a kitchen towel and let it rest for 1 hour. Flip the dough in the bowl, so that the top of the dough is now on the bottom of the bowl and let it proof for another 45 minutes, covered.

Turn the dough onto a lightly floured surface. Divide the dough into 6 equal pieces and roll each piece into a round ball. Place the 6 dough balls onto a lightly floured surface, gently cover the dough balls with a towel and let them proof for another 20 minutes. 

Roll each dough ball into a log with tapered edges, about 12 to 14 inches long. Place each log with the seam side down on the counter. Take 3 logs and place them vertically parallel to each other in front of you. If using flowers, vegetables or herbs for a seasonal challah, lay them equally and vertically on each log of dough. Braid the 3 logs of dough (with the seasonal ingredients if using) into a 3-strand braided challah (tuck the seasonal ingredients into the dough as you braid the challah). Repeat with the remaining dough logs forming another challah. Transfer each challah onto a parchment paper lined baking sheet. Gently cover with a kitchen towel and let the challahs proof for 1 more hour. 

Preheat the oven to 355 degrees F.

Beat 1 egg with 1 teaspoon of water and ¼ teaspoon of salt to make an egg wash. Remove the towels from the challahs. Brush each challah with the egg wash. If using seasonal flowers, tuck them into the seams of the challah at this point.

Transfer the challahs into the oven and bake for about 27 to 30 minutes until golden brown, rotating the baking sheets halfway through.

Serve warm with a side of tahini and/or olive oil.